Tianjin's Natural History Museum holds one of the better dinosaur collections in northern China, with full skeletal mounts including specimens excavated from the surrounding region. The paleontology galleries are the highlight: the region around Tianjin and Hebei has been surprisingly productive ground for fossil hunters, and several specimens here are not replicated elsewhere.
Beyond dinosaurs, the museum covers geology, marine biology, and Chinese flora and fauna. The building is large enough that a proper visit takes two to three hours. It tends to be quieter on weekdays and is a reasonable option if you have children in tow or bad weather to escape.