The Map With One Thing Wrong

A map turned up that is perfect except for one building nobody has ever seen. Name what the building is.

Concrete common nounSomething you can see, hear, smell, taste, or touch: bandstand, chapel, boathouse.Adverb (when)Try at once, repeatedly, or before dawn.Progressive verb (the -ing form)The -ing form: measuring, listening, waiting.Adverb (how)Try thoroughly, pointedly, or as expected.Collective nounA word that names a group of people or things: murmuration, scatter, delegation.Adverb (how)Try neatly, pointedly, or all facing one way.

6 down, 5 to go

Subordinating conjunctionTry although or though.Preposition (where)Try inside, beyond, or around.Descriptive adjectiveTry weathered, sodden, or council-issue.Descriptive adjectiveTry unremarkable, waterlogged, or vast.Adverb (how)Try all at once, warily, or in silence.

Every blank has to be filled before this one can finish. Let's go.