Unique Encounter Area: the Shrine to Ethics

[Last submission to Kalibruhn, and the only one playtested in my South Province D&D campaign]
The Shrine to Ethics

Word has only begun to spread about this location along a lonely stretch of road in the hills. No one knows the identity of its builder, though it is clear that the man was a spellcaster of some sort, and that the shrine was not here more than 25 years ago.

The shrine consists of a curved, roofless, stone wall eight feet tall and ten feet in diameter. There is a wood and iron bench, uncomfortably tall, chained to the inside wall. In the middle of the shrine is a well. The well's three-foot high retaining wall is made of the same limestone as the rest of the shrine. Except for a wooden bucket on a rope on the edge of the well, there is nothing else in here -- no icon or holy symbol of any kind. The average traveler may think the shrine has been robbed by sacrilegious bandits, but such is not the case. Its builder apparently intended it as a test of certain virtues.

The first virtue tested is trust. There is a plaque on the inside of the well, just under the rim, that reads, "The suspicious will not drink here." Its logic has thwarted many a traveler from a cool, refreshing drink. What's more, the water in the well is magical, so that anyone drinking it will be able to read invisible writing on the wall that reads, "The merciful will enjoy their rewards." Then a large fire salamander (the animal, not the extraplanar monster) scurries up out of the well and moves threateningly at anyone in the shrine. It squirts acid, but automatically misses unless it is attacked first. If no one makes any move to attack the salamander, it looks up and speaks, saying, "This is the reward for your show of mercy. If you will toss a valuable gift into the well, I will give you something in return." This is the third test, for generosity. If something of great value (relative to the finances of the traveler) is tossed into the well, the salamander will scurry back down and fetch it. But when the item is returned, it will be more valuable than before. If no such sacrifice was made, then a fire salamander three times the size of the first one emerges from the well and attacks.