DUP36 is probably not a spot where you’d go every day, but if you happen to be there, it’s also an experience you probably don’t experience every day.
After walking down the stairs, you’ll enter a great space with walls filled with books, a lot of books. It also looks a bit like an old cinema. DUP26 is a multipurpose place, which is a secondhand bookshop and refurbished furniture shop during the day. However, it doesn’t offer many books in English, so either you can be satisfied by buying some book in Czech (or choose one of the few in German or Russian) or choose some old postcards or LP as an original souvenir. In any case it won’t deplete your budget as all the books have a fixed price of 5 CZK, which sounds like a joke, and the LPs and others aren’t expensive either.
If you are lucky, or have checked the programme in advance, you can listen to a concert or reading, enjoy some other event or just experience this unusual underground spot just a few steps from Kafka’s head near Národní třída metro. Just carefully follow the map as the entrance is not well labeled.