Bothies
Remote & free
Bothies are primitive huts or mountain shelters that are usually in remote places, never locked, always free and not bookable.
You may have them to yourself or be nose-to-tail with other visitors.
Facilities also vary a lot, but it's best to assume you'll need all camping supplies except a tent.
Most bothies are managed by the Mountain Bothies Association who maintain an online map. There’s another useful