At a local swimming pool there is a path that runs the middle of the pool about 3 inchs under the water, on the right side of the path there is a rail about 2/3 inchs above the water and about 1/1.5 inchs in diameter.
During the day there are millions of people so 'rail sliding' is out of the question but when it starts to get dark you get the pool to yourselves. Seriously you can slide about 20ft maybe 30ft depending how good you are!
Had to reduce the quality because of 30KB limit but i thought i might share it with you anyway. Hope you like it