Sky Tower at Leighton Moss: gravitational potential energy

We were able to go up the new Sky Tower on the RSPB nature reserve at Leighton Moss near Carnforth. It is 9 metres high. I had to do work against gravity to climb it. Suppose my mass is 100kg. That means that my weight is 10x bigger on Earth - weight meaning the pull of gravity on my mass. So my weight is 1000N. I do work against this 1000N force. Work done = force x distance moved = 1000N x 9m = 9000J of work done. This then becomes the energy stored by climbing - gravitational stored energy. I can get that energy back when I come down.