Perfect for what you want would be he cave above Dove Crag (Ullswater) which sits right above a 300' drop. As you approach look for a dark horizontal slot above the scree up and right of the main crag. Looks inaccessible but its just a walk. A bit more than an hour from the valley. Hard to find in the dark. Comfy, usually dry and awesome view down the valley. You could approach it via the N. Ridge of St Sunday crag, one of the best scrambles in the Lakes - via this approach you might get there in daylight in June but you would have to be motoring.