Nearby the village is a large lake said by the villagers to contain a water god. They tell the party that if they want good luck on their journey they should hire a boat and go to the center of the lake and give a donation to the god.
Unscrupulous characters may realize that if people have been giving donations for awhile, there must be a fortune just sitting there under the water. The water may really be inhabited by a god, or perhaps just some dangerous water bound creatures, an elemental perhaps. Either way, there is a reason that others haven’t claimed all the wealth.