To enter the premises, one may step through the window of what appears to be a red-bricked, condemned department store called Purge and Dowse, Ltd. The interior, on the other hand, looks exactly as a hospital should. One way one individual can enter the building is speaking to an apparently inanimate dummy in the department store. (Credit to HP Wiki)

Founded by the Crowdy family shortly after the death of Maximilian Crowdy, then Minister of Magic, in 1781. Inaccessible to muggles, the library is located about a block from the Ministry of Magic Headquarters. The first three floors are open to the public, boasting reception and literature, reference texts, and public records, respectively. The subsequent five floors are grouped by subject matter, and accessible only to Ministry employees with the appropriate clearance level, or members of the public who have received permission from the Department of Magical Education for a particular use. Such petitions take from two to ten months to receive word on.

Located in London, The Museum of Magical Miscellany is reachable through a secret door in a regular, muggle museum. Filled with exhibits on everything from Ancient Rome to the muggle riots of 1877, the museum is massive and winding, and has statues, artifacts, and paintings, all related solely to wizarding history. Visitors may berate resident ghosts for historical details if they are so inclined.

A pub located behind a magical door, the Augurey is named as such due to the severed beak of a long-dead augurey located behind the bar. It's drearily decorated, but has cheap drinks. The owners are notoriously uncaring and let all manner of strange leftists hang around for hours.

A special wing of the National Portrait Gallery, the space can only be accessed by caressing a specific panel with one's wand in the muggle section of the building (though, fortunately, in a little-trafficked area of the building). It boasts several chambers of magical portraits, as well as a small ballroom, the walls of which are painted to convey various themes depending on the time of year.