The King's Observatory

 A roof with a view - over the golf course that now surrounds it. Apparently not only the pagoda in Kew Gardens but also the Shard can be seen through gaps in the foliage of a nearby tree.

The stairs are narrow, but Queen Caroline in the wide skirts of the time came up them, along with 15 other people, to attempt to see the planet Venus cross the sun (which took about 8 hours and was being carefully observed all over the world).

Putting down the covers made more standing room -

... but it must have been quite crowded ...

The telescope isn't original, it's just there to give some sense of what the observatory was like -

Several lovely bits of old ironwork that opened the viewing aperture and turned the entire roof to position it -

And candlesticks for (faint) lighting, so as not to dim the view of the stars -