Meet up with friends, watch series/films, listen to music, play a boardgame/computer game, do some adult stuff, go to a museum, take a nice walk, go cycling; lots of options tbh
It really depends on where you live. When it's warmer I go with friends to a train bridge, we wait to the train to come and then we jump off into the water. It's like a 10m fall, a bit scary at first but so much fun.
Go to the beach. I live near lake Ontario though.
Have a bonfire with some friends.
Just go outside after dark, (I usually go to the park), chill, talk with friends, look at the stars.
Go to your high school house parties.