I found it in the forest but I've never seen anything like it so I took it home to see what it is. Does anyone know?
This is a caddisfly larvae (Trichoptera). They live in streams and other water that are rich in oxygen. They protect themselves by building there own 'house', with whatever is available, e.g. plant or wood fragments, gravel or even snail shells (see picture below)
Picture from Dutch wiki
Id to species level probably requires microscopic work.