Greenwich Observatory i) A brass line stretches across the courtyard, marked with the names, latitudes and longitudes of various world cities.
ii) There's a big silvery sculpture at the northern end of the brass line, consisting of a pole inclined at 23½ degrees to the vertical, an equatorial ring and two segmented sails (pictured above left).
iii) A tall stone plaque (with a vertical black meridian line) is set into the wall immediately beneath the observatory courtyard. A short brass line continues across the higher of the two footpaths.
Greenwich Park iv) At the foot of Greenwich Park is a banana-shaped boating lake. The zero degree line cuts straight across the middle, making this your big chance to pedalo along the meridian. On the northern bank lies a raised circular platform supporting a big triangular sundial (shown in the photo above, at noon Greenwich Mean Time with the sun's shadow pointing due north). This is the Millennium Sundial and, like a certain other local millennial project I could mention, it's fatally flawed. The architect was given the wrong information and the sundial ended up being built 2 metres off the meridian, so it runs 8 minutes adrift. They should have built it dome-shaped.
Maritime Greenwich v) On the first road north of the park, a plaque built into the wall of The Chantry reads 'Prime Meridian, zero degrees longitude'. A downward-pointing arrow divides East from West.
vi) North from the plaque there's a row of ten raised studs following the meridian across the road (pictured above right) before disappearing into the front room of number 2 Feathers Place.
vii) Old Woolwich Road School lies bang on the line, and so has been renamed Meridian Primary.
viii) The meridian crosses the grounds of Trinity Hospital, a retirement home for 21 local gentlemen and the oldest building in Greenwich.
ix) The green meridian laser passes directly between the four tall brick chimneys of Greenwich Power Station. This coal-fired station was built by London County Council in 1906 to generate power for local trams. More recently it was used by London Underground as a peak-time back-up station, before finally being mothballed last year (just in time for a serious power cut).
x) The meridian enters the Thames totally unmarked at Crowley's Wharf, a few metres west of the nasty modern development at Anchor Iron Wharf. Steps lead down to the beach (yes, the Thames has beaches) from which the meridian heads off north across the river, just missing the giant derelict coal jetty sticking out from the power station behind. Next stop, the Dome.