This excellent, oft-overlooked museum, opened in 1898, is devoted to the history of Prague from prehistoric times to the 20th century (labels are in English as well as Czech). The museum reopened in 2025 after a long renovation. One of the many intriguing exhibits is Antonín Langweil’s astonishing 1:480 scale model of Prague as it looked from 1826 to 1834. The display is most rewarding after you get to know Prague a bit, as you can spot the changes. Look at St Vitus Cathedral, for example, still only half-finished.
The Florenc building is the main branch of the museum, but it also administers 13 other sites, including most of the city's medieval towers. Check the website for the current status, open hours and admission prices.