Greenwich - the Observatory
& the Seaman's Home

In Greenwich, you really can know what time it is. And yes, unlike the contention of the Chicago song from about 1970, one really can know the time; the measure of time works within a consistent rationally constructed system whose rules can be accurately described.
Greenwich Time takes on its importance because one day a sea captain realized that, if he knew the time in Greenwich (good chronometer required) and knew the time where he was (determinable by measuring the sun's distance along its daily path), he would know how many miles east of Greenwich was his ship. As this clock & the accompanying models of British measuring units are out in the weather, I assume more secure instruments keep the official time and measures, but these are the ones the tourists get to enjoy.
There are two, matching, spires on Wren's Seaman's Home
The "clock" on one is a clock; that on the other indicates wind direction.
The highlight of the home (which for over 100 years served as hospital and home for pensioned and disabled British seamen) is the Painted Hall. It was conceived as a dining hall, but officials soon found it preferable to reserve its use to special occasions (we were told the old sailors sometimes staged food fights & the like, a mode of behavior quite out of keeping with the surroundings).
And these are shots from the Chapel.
The raised pulpit makes me think of Moby Dick, though Melville's Father Marple mounted the pulpit via a rope ladder rather than a circular stair.
This curious little dome houses a staircase that leads to a tunnel beneath the Thames. Perhaps it is time for us, imaginatively, walk that tunnel, or better, let us boat to the Tower Bridge and the Tower of London.
  Greenwich 1 / Greenwich 2 / Thames & Tower of London / Avebury / Regents Park / Trafalgar Square