The Holtenau locks mark the Baltic entrance to the Kiel Canal, where ships are raised or lowered by about half a metre to match the different water levels of the Baltic and the canal. There are two pairs of locks — the older pair built in 1895 and a larger pair opened in 1914 — and they operate continuously around the clock, processing an average of 80 ships per day.
The viewing area on the northern bank is free and open at all times. Wooden benches give a direct view along the lock chambers, and the ships that pass through — bulk carriers, car transports, tankers, and occasional naval vessels — pass close enough to read the hull markings. Waiting times vary, but if you stand for twenty minutes you will almost certainly see at least one lock transit.
Holtenau is a residential suburb about 6km north of central Kiel. Bus lines connect it to the city centre, or it makes a reasonable cycling detour along the fjord path. A small footbridge crosses between the lock chambers on the southern end.