A standard roleplaying environment: the tavern. This is another easy one to create in your own home, providing you have a large enough group of roleplaying friends. Let us assume your PC group is no larger than five, and that the rest of your friends can be NPCs. Let us also aim for an exceptionally seedy and unscrupulous city tavern.
In a good LARP it is desirable to separate the players out individually at some stage, because they are more suggestible and afraid when they are alone. Some form of individual challenge is probably the best way of doing this. One possible setting for this is a cave system, and it is probably one of the easiest to recreate realistically, and one of the most perfect for playing on fears of claustrophobia and darkness.
In the middle of a desert in an oasis is a single prospering oak tree. Near the tree is a large pool of water. Drinking from the water is said to give you eternal life but really only extends your life for as long as you continue drinking from it. Those that have found it and left, have never found it again. Some search for it still.