A lift lock works pretty much like an elevator - there is a basin that the boats drive (navigate?) into, the doors close and then a set of counterweights is engaged to bring the basin up or down. (At the lift lock in Peterborough, there were two separate side-by-side basins, one lower and one upper, that served as natural counterweights).
A group of kayakers joined us on the way up. We were all eagerly awaiting the start of the ride!
What I find amazing is that the technology has not really changed since the 1930s when this lock originally went into service. A few improvements have been made, but it's basically the same structure and the same core idea. A new lock is being built alongside this one as this waterway gets quite busy and needs to accommodate large ships, but the historic lift lock will remain in service for at least another fifteen years.