Built in the 19th century when the Prussian rail network was pushing through this part of Poland, the Gniezno Locomotive Depot is a protected historical monument and one of the more unusual things to see in the city. The brick roundhouse and associated engine sheds have survived largely intact, and a number of preserved steam locomotives remain on site — the kind of heavy industrial heritage that tends to disappear quietly when it stops being economically useful. Here it didn't.
The depot speaks to a part of Gniezno's history that has nothing to do with medieval kings or bronze doors: the city as a functioning railway town under Prussian administration, connected to a wider industrial Europe. It's worth the short walk from the centre if you have any interest in railway history or industrial architecture. Opening hours are limited and the site is not always accessible, so it's worth checking ahead before making a special trip.