This is a great article posted on another site (who reposted it from another site, who took it from another), but I thought many would enjoy it here. It is The Lazy Man’s Guide for Constructing a Call of the Cthulhu Adventure, written by Sandy Petersen, original author of the Call of Cthulhu.
at a place were magic gathers, for what ever reason, the trees of this place produce fruit that is filled with magic energies . these fruits when eaten cause different effects. much like the potion a wizard makes.