Do I need to bring my sleepingbag or sheets ?

Sheets are included in the price, but ofcourse you can bring your own sheets or sleepingbag.

Towels you have to bring yourself though or you rent them from us.
Costs are SEK 50:- per set. (1 big and 1 small towel)

Do I need to book a bed or a room or can I just hop-in at Folsom ?

You have to book at Folsom. You can not just hop in.

What is the check-in time and when do I have to check out ?

Check-in time on the day of your arrival is between 14:00 and 23:00.