Grottos are places of worship and prayer, they are usually devoted to a saint or two. You can go to a grotto to read, pray, do nothing but think, and etc. A grotto might also have a plaque that givees information on that saint. Go here for real information.
The word grotto means:grot·to (grt) n. pl. grot·toes or grot·tos
1. A small cave or cavern.
2. An artificial structure or excavation made to resemble a cave or cavern.
So if you live near a grotto or go to a church that has one go to and da what you would like to do.