They're called parks and libraries. Give em a try sometime. You can totally just be there. Doing nothing.

Also see: trails, walking paths, riverwalks, nature preserves, university campuses, museums (at least the lobbies), scenic overlooks or viewpoints, benches outside public buildings, beaches, town squares or a plaza, walking down a "main street" or downtown area, lakes, ponds, community gardens, a fucking field.

I have partaken in every one of these before without notice, payment, urgency, solicitation expectation or anything other than just being.

Also there's shitloads of free community groups for every hobby out there or idea. Especially if you live in or near a decent sized town.