This plot is a low-combat (no combat hopefully) test of the players ingenuity and other skills. It described for a medieval period but could easily be transported into most settings.
Outline: The players have a treasure map for stolen gold but on finding the place, discover an inn has been built over the spot where the gold is buried. The map describes the location of the treasure as 20 paces towards the river from a gnarled willow, 2 feet beneath a large flat stone. This is now manifestly beneath a room in the corner of an inn built on the river flat. The room is dirt-floored and windowless, being used by the innkeeper as a holding cell for guests that have exceeded their capacity somewhat and are in need of protection, or have become belligerent and a nuisance to other customers. The innkeeper is scrupulously honest and does not "roll" such guests but will extract payment for any damages. The underground cellar of the inn narrowly missed uncovering the gold, being under the adjoining room and an excavation from the near wall would find the treasure after only a few feet of digging. On the other hand, the innkeeper is not in the habit of letting guests into his cellar!
Background detail. This outline is particularly set up for characters who have set themselves up as "the good guys" as it potentially involves an ethical dilemma if your players enjoy such things. Location. The Inn is situated on a route junction where a side stream enters the main river. 2 days up river is the city where the gold originated. The main route enters a hard gorged section of road below the inn and 6 further days of travel brings the route to a major port city. The other route continues up the side stream and over a low pass after a long day's travel in lonely country. Another day's travel is required to arrive at the small sea port where the characters will start from. This port town has grown enormously in the last 12 years since a pirate kingdom was destroyed allowing trade to flourish in the southern ocean. Consequently this side route has grown much more important allowing the inn to flourish. The innkeeper was a smithy by trade and his services are valued by travellers. The inn stands by itself with no neighbours or other business in very underpopulated country which makes it something of an oddity in the world setting. History. The gold is a booty from a raid on a goldsmith's shop in the up- river city 13 years ago. It was a bulk purchase to be shared with other goldsmiths in the guild and was guarded by an apprentice whom the thief killed, leaving a widow and 3 children. The thief ran into trouble though with a lame horse near the inn site, and with the hue and cry close on his tail, he buried the gold under a large flat stone before fleeing up the then little-used trail to the small port. He covered his digging further by piling all the excavated earth (a distinctive red) onto his cloak, then emptying it bushes nearby. His luck really ran out though when he arrived at the small port and was arrested by the guard for an earlier murder and was summarily executed. He did however have time to make the treasure map and gave it to his lover, mother of his 2 year old son. She would not have a bar of what she correctly guessed was stolen gold though but is now very sick (beyond the means of the characters to cure). Her son, now 15, is desperate to help her and has approached the party with the map. They could be relatives or friends of a party member and the gold would be used to buy a cure. In the provost's party, pursuing the thief was the murdered apprentice goldsmith's brother, a journeyman blacksmith. The party stopped at the route junction on finding the lame horse while woodsmen in the party tried to find which route the thief had taken. Answering a call of nature in the bushes, he found the pile of red earth but told the provost nothing. After it was discovered that the thief had already been executed but without any gold being found, he made a shrewd guess about what the thief had done, but failed realise that the earth had been moved into the bushes which he now turned over in what rapidly became an obsession. To cover his activities, he built a small smithy to service travellers coming up the gorge road, which soon became augmented by an inn as the trade in the southern ocean made the route to the port town more important while his digging was unfruitful. He even now hasn't given up on finding the treasure though he seldom is actively digging. His strange obsession (which he wont reveal) means there are light-hearted stories about him searching for a rainbow's end, told at his expense by frequent travellers stopping at his inn. The innkeeper is well-liked and married when his obsession cooled, now having 5 children helping around the inn. He has also taken in his brothers destitute widow and children who help out about the inn. The widow helps cook and brew but this is a bitter come-down from her expectations in marriage to a goldsmith and she frets for her 16 year-old daughter now serving behind the bar. Her older sons are competent smiths under the innkeeper's teaching. The family all share the secret about the possibility of gold buried nearby but none take this seriously. The challenge for the players is compounded by fact that it would be very unusual for anyone to stay more than 1 night so 2 nights without an obvious excuse. This will result in some pretty blunt queries and suspicion of "casing the joint" from people used to fending for themselves in an isolated spot. Stories about the innkeeper's strange diggings will be easily heard but no one suspects what he is after. A reasonable number of people, many on very good terms with the keeper will be present on any night, though all will be passing through.
If players come up with an ingenious scheme for getting the gold out and clear, then good for them but I would be likely exploit any weakness in their plans to set up a confrontation with the keeper and the widow. They are very unlikely to try force unprovoked but will certainly put forward an impassioned case for their rights to the gold - better life for daughter and sons, years of graft, etc. Obsessions can be dangerous things though ...