3D print Venice
A city built entirely around water, which makes it an unusually direct test of how well canal and coastline data hold together in a model.
Venice has no roads in the ordinary sense — canals do that job, and OpenStreetMap maps them as waterways rather than coastline, so they come through as thin channels threading between densely packed building footprints rather than one large reconstructed sea. The San Marco basin, where the Grand Canal meets open water in front of the Doge's Palace and the Campanile, is the widest and clearest stretch of water in the city and a good anchor for a first model.
The Doge's Palace itself — Gothic arcades facing the lagoon, a courtyard behind — is dense enough in ornament that it reads clearly even at a small scale, right at the edge of the basin.