Go through the Enrichment Activities Page and pick out a topic that you're passionate about and click on the various links, even if they are not your age level.
To strengthen your brain, visit the Creative/Critical Thinking page and do some logic puzzles.
Invent something new out of items that you have in your house.
Get out and walk/exercise and enjoy/observe nature.
Activity Hero Summer Online Camps
Activity Hero Summer In-person Camps
IEA Summer Classes - Institute for Educational Advancement
Belin Blank Jr Scholars Academy