Whatever floats your boat - the place with two ship lifts and two giant locks.

Dortmund is a port despite being a long way inland. The Dortmund Ems Canal is a 269km (167 mi) ship canal that connects the city to the sea. At Henrichenburg, ships needed to be raised 14m and over the years, there have been four different ways of doing that: two lifts and two locks.
The oldest lift is now a museum. I visited in March 2022, travelling from Dortmund using public transport.
Visiting:
Use the planner at bahn.de or in the DB app. This will also tell you the ticket you need to buy. Every other mapping service seems to think it takes three hours, mostly walking!
Adult admission to the old ship lift is €3.50. The lower level (except the float shafts) is accessible, and there is a lift. Ramped access to the Oberwasser level is available, but you need to ask for the gate to be opened. For the other levels, there are an awful lot of steps.
The locks and new lift are part of an industrial heritage park which is free to enter. There is an admission charge for the exhibition at the new lock. This wasn't open on the day I visited even though it normally would have been.

[@streetrambler134]

Great video, loved the sign saying how many steps up, medium challenge and hard challenge. I think you definitely deserved that lovely beer too.