Squatting abandoned places
It is quite possible in many places to find abandoned places to sleep in or stay for few days. It's for example remarkably easy to find abandoned buildings in the Balkans.
Try to find an abandoned buildings, house, or whatever. Look for a place that it's not too easy to find so you're not disturbed during the night. Try to find a clean place, and be sure that the structure is strong enough, stay safe.
It's free and can be a great alternative to camping if you need a roof, to escape a too hard weather for example. It can also be fun to discover abandoned places.