LOCK 21...Peterborough...one of the world's largest pan locks. Designed to lift or drop boats 65 feet in two water filled tubs. Movement in one chamber must force and equal and opposite movement in the other chamber. Each chamber holds 3 million 400 thousand pounds of water. That's a whole *&%$load of water....and can I just say, all my worries were for nothing. It was actually quite fun...smooth ride up for us....and yes, that tourist figured out our camera. I thought we got some great shots. We began to look forward to Lock 35 at Kirkfield Pan lock...the 65 foot drop.