movie where a group of friends go to a retreat for the weekend. They have to take a boat their (a paddle boat I think) They get there and have no electricity. They drink and party and find a bar in the building (a girl ghost haunts it). They also go on a hike and find a small cave and mess around inside for a while. They go back to the retreat and ultimately end up trapped inside. There is a man outside but he cant see or hear them banging to get out.