Where can I take my ultralight aircraft?
Taken from a more specific answer by @Pondlife to a question about ultralights and National Parks:


  For ultralights specifically, the regulations are in 14 CFR 103 which has only a few very simple restrictions on where ultralights can operate. 103.15 says you can't operate over a congested area or a crowd of people and other restrictions are the obvious ones: don't fly near airports without ATC approval, don't enter restricted airspace, and do follow NOTAMs.