Did ancient peoples ever hide their treasure behind puzzles?

The treasure of the Knights Templar is a case in point. Not the one they left for Dan Brown to find out; the one they dug out by apparent accident, which we now call money multiplier. I have no idea what name they had for the thing, nor if they were even conscious they got hold of a treasure in the form of actual, physical, solid gold coins. This however, as Robert Columbia pointed out, is not the puzzle; it is the treasure. The OP required also the treasure to be guarded by an intellectual challenge, and a "jungle puzzle" look and feel of the unlocking protocol.

In the present case, the intellectual challenge is: how do you make mortgage loans a profitable business in a context where slicing the banker alive in the episcopal palace is a socially acceptable, if illegal alternative to defaulting? And how do you collect deposits in the first place, when retirement planning usually reduces to dropping coins in a secret chest one at a time, deep down in one's own garden? The stroke of genius is in the solution: on the collecting hand, disguise your banking activity as currency exchange, and issue maturities masquerading as traveler's chèques. On the other, loaning hand, disguise your interest loans as sharecropping contracts. All this without either saying "fractional reserve" aloud, nor telling outright lies to your customers.

As for the "jungle puzzle" look and feel, it is corollary to the solution: to keep exchange services in high demand and income in fatty amounts, you must build ships, bulwark a bridgehead in Holy Land, deploy supply lines over the Mediterranean sea, op-research the schedules of the shuttling ships, trim their cargo, sails, and course, dodge storms and squirts of Greek fire, fill log books, quarantine the sick, cook for the healthy, fill immigration forms, patrol the desert in steel combat boots, fill accounting books, balance them, carry them around in auditing campaigns & what not. And you, the would-be banker, cannot subcontract this jungle crawl while presiding boards of directors in the 13th C. equivalent of tailcoat & silk hat; you must exert your own person to each of those tasks from the noblest to the meanest, on pain of acquainting nosy outsiders of your private agenda.

The Order of the Knights Templar (OoKT for short) is known to have issued promissory notes against deposits in cash minus brokerage fees. Overtly or not, these notes were managed as maturities. If covertly, that is, if no maturity date was mentioned on the note, one would be implied if they were only payable in a designated town: the implicit date being set by the duration of the physical trip the note had to survive to reach its point of payment. Hence the importance of barring the average pilgrim or colonist access to fax, or rather to the nearest 13th C. approximant. .

The consequence is, the OoKT must have soon noticed each of its exchange offices was squatting on a heap of gold of roughly constant thickness and computed that, at whatever office it showed an inclination to dwindle, this would be linked with an increased popularity of the town among tourists. Hence, the dwindling could be controlled by writing an explicit maturity date on the notes; e. g. under the pretext that secure gold transfer to that specific office is slower if every ship heading to it is full to the rim with passengers of unknown probity.

The next thing any banker in the OoKT's shoes would take notice of is, if each and every gold mattress entrusted to them has constant height over time, then gold transfer is not needed at all: so, transfer authenticated balance sheets instead (those are needed, to beacon the managers of the exchange offices to the path of righteous poverty), which can be secured at much lower cost. The provision for hijacked or lost ships thus dropping by 90%, the broker can now pocket an equal portion of the exchange fees, and make a cosy income of what was originally a minimal indemnity against the risks in his business. This however is not the actual treasure; merely the tip for the clerk and the teller.

The 3rd thing is to secure said mattresses against robbers, which as any banker will soon reflect, easily obtains by converting them to something several times heavier than a robber; to wit, real estate. This is how bankers discovered again and again that, for better and often for worse, opening credit in excess of one's reserves amounts to creating actual, physical, 79Au money out of nowhere. This, in my view, is also how Philip the Fair discovered to his dismay that the actual, physical, 79Au-based wealth of the Order litterally flew up the chimney when he sent them to the stake.

The OP only requires the jungle puzzle to appear as a deliberate setup authored by whoever buried the treasure, to select the worthy by intellectual challenge. Who did this in the case of the OoKT is anyone's guess; mine is, in long format, twas none other than Lil' Geez' o' Nazar'; witness, extant hints to the place of burial, cf. Matt. XIX:21; "go and sell that thou hast, and give to the poor, and thou shalt have treasure in heaven: and come and follow me. " Which the founders of the OoKT diligently did; only they correctly reckoned that once the Kingdom of Heaven tranferred its capital from Beloved City Up There to earthly Jerusalem down here, its central bank would follow, and down with it the promised treasure.

If this seems far-fetched, try Pope Gregory as the treasure-burier. He advocated the Jews be left free to mind their business; which traditionally includes pawnbroking and other financial services. So there might be a 1.3kyr old note describing the benefits of fractional reserve policy, somewhere in the Vatican secret archives. In short format, I don't have a clue, so your pet theory is welcome. Preferably if, unlike mine, it is backed with actual archives, secret or not.

The Egyptian labyrinth(s) could possibly be an example of actual treasure hidden behind a puzzle.

I had a little difficulty finding a source that "felt reliable". This tantalizingly detailed description:

You entered the maze from a descending stairway, hidden on the south side of the pyramid, which led to a small chamber. This apparently led nowhere; the hidden exit was in the roof of the chamber, which concealed a sliding stone trapdoor. This led to an upper chamber that opened into a wide passageway completely filled in by massive stone blocks. One thief had laboriously carved through these blocks, only to discover he had been tricked—the passageway was a dead end. The correct path was a corridor closed only by a wooden door, which opened into a dead-end passage; to get out of this passage you had to find a hidden sliding stone. The sliding stone opened into a bare room; from here a secret trapdoor led to a long passageway. This passageway was filled in with massive stone blocks at its far end, which suggested it might lead somewhere important; even better, two open burial shafts gaped in its floor. One of these shafts was completely filled in by stone slabs and thus seemed like it might have concealed the burial chamber itself, while the other shaft appeared to be empty. The correct route was actually a secret door concealed back in the middle of the long passageway.

isn't very well sourced (here) and the site seems a little more geared toward entertainment than archeology. Egyptian history attracts a lot of ... let's call it "enthusiasm".

Another source I found looks to be a little more healthily skeptical of some claims about labyrinths' descriptions. Herodotus described a labyrinth, but Petrie, who claimed to have found it, might have been wrong:

The case of Amenemhet III's funerary temple being the labyrinth is circumstantial at best. There is no trace of the funerary temple's plan, only its perimeter. It is not located at the corner of a pyramid, nor does it have underground chambers. The only evidence in its favor seems to be its questionable proximity, about 15 miles, to a lake called Moeris (the neighboring Crocodilopolis is not compelling as several other towns bore the same name). For the lake shore to reach the temple, Medinet el Fayyum would necessarily be submerged. It may well be that the labyrinth described by Herodotus and other ancient writers has not been discovered, and lies yet hidden somewhere beneath the desert sands.

Here's what Wikipedia says Herodotus says about the Egyptian labyrinth:

It has twelve covered courts — six in a row facing north, six south — the gates of the one range exactly fronting the gates of the other. Inside, the building is of two storeys and contains three thousand rooms, of which half are underground, and the other half directly above them. I was taken through the rooms in the upper storey, so what I shall say of them is from my own observation, but the underground ones I can speak of only from report, because the Egyptians in charge refused to let me see them, as they contain the tombs of the kings who built the labyrinth, and also the tombs of the sacred crocodiles. The upper rooms, on the contrary, I did actually see, and it is hard to believe that they are the work of men; the baffling and intricate passages from room to room and from court to court were an endless wonder to me, as we passed from a courtyard into rooms, from rooms into galleries, from galleries into more rooms and thence into yet more courtyards. The roof of every chamber, courtyard, and gallery is, like the walls, of stone. The walls are covered with carved figures, and each court is exquisitely built of white marble and surrounded by a colonnade

The "baffling and intricate passages" bit hints at a labyrinth designed to confuse, but maybe it was just labyrinthine to Herodotus.

My preliminary conclusion (especially after reading (well, skimming) that second reference) is that I currently have no idea how much of what people say about Egyptian labyrinths and their purpose is real, but it might be a fruitful path for you to explore if you want definitive proof of "treasure behind a puzzle" in antiquity.

The Copper Scroll

The Copper Scroll is a Dead Sea scroll found in 1952, unique in that it is of copper (with a little tin), has a list of 63 or 64 locations of treasure with "obscure hints of the locations".

Although it was initially disputed whether or not the list was historical rather than legendary, a

scholarly consensus seems to be emerging that the Copper Scroll is an authentic record of ancient treasure, to be dated around 68 c.E., and that its treasure belonged either to the sectarians of Qumran or the temple in Jerusalem.

Source: Al Wolters, 'History and the Copper Scroll' (Annals of the New York Academy of Sciences, 1994)

Strip of the Copper Scroll from Qumran Cave 3 written in the Hebrew Mishnaic dialect, on display at the Jordan Museum, Amman. Attrib: Osama Shukir Muhammed Amin FRCP(Glasg) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]:

The scroll is also different from other Dead Sea scrolls in the language it uses and in its contents. Notably, it is not a work of literature and there are no legendary-type stories in it; rather, it is an inventory of hidden treasure with some quite detailed descriptions (in part) of specific location. For example,

In ‘The Ruin’ which is in the valley of Achor, under the steps leading to the east (at) forty half-brick cubits: (there is) a chest of silver and its vessels, a weight of seventeen talents.

However, much remains unclear; in particular, both the original source and the quantity (definition of a 'talent') of the treasure are disputed by scholars.

None of these treasures have yet been found. On the difficulties,

The solution to the enigma posed by this scroll is no doubt to be found, at least in part, in the precise study of the text: its topography, the identification of the important site of Koḥlit, and the meaning of the Greek letters: symbols, or rather coded anthroponyms of the individuals in charge of certain repositories.

Source: Émile Puech, 'The Copper Scroll Revisited' (2006)

To what extent the scroll is a genuine puzzle is, admittedly, debatable in that it may have been intended that only a specific individual (the person who hid it) could find a specific location unless he actually revealed key information to someone else. At any rate, it is likely, given the vagueness of the directions to the starting point of the search, that only someone with a detailed local knowledge of the landscape and buildings could find the locations listed in the scroll. It has also been suggested that a second document is needed to find the treasure as item 64 on the list says:

Item 64: In a pit adjoining on the north, in a hole opening northward, and buried at its mouth: a copy of this document, with an explanation and their measurements, and an inventory of each and every thing.

It may be argued that, on the basis that nothing has been found, the treasure is imaginary. However, the fact that the text of the scroll is very difficult to interpret (particularly given changes to the landscape over the centuries) is a major hindrance. It has also been suggested that the treasure was found centuries ago - by the Romans.

One man's lock is another man's puzzle.

Combination locks have been used since at least ancient Rome. Whether the lock uses numbers or letters (or other symbols), the combination to be entered may be set based on a riddle or some other piece of knowledge as a mnemonic. The lock is meant to be solved at some future time by someone who has the correct knowledge. The intention of the one who put the lock on was most likely that it only be "solved" by authorized persons, but to a thief it is a puzzle to crack. Lockpicking is as old as locks themselves, and while mechanical solutions are probable--it is likely the codes were sometimes cracked as well.