Paul Terry wrote:
When walking through the tunnel under Exhibition Road, from South Ken
station, I have often thought how very much like a small rail tunnel
it seems.

Now I have just come across an 1873 map (Collins' Standard Map of
London) in which the tunnel is shown extended NW under Prince Consort
Road to terminate at the Royal Albert Hall - and the route is marked
as a "railway under construction".

Does anyone know anything about this? Was it to be a short branch off
the District, or a self-contained shuttle? To compound the mystery ...

http://www.imperial.ac.uk/estatespro...nel_safety.htm

... mentions a tunnel complex under the South Ken campus of Imperial
College. Is this part of the same system?

Alexander Edmonds in "History of the Metropolitan District Railway Company
to June 1908" only mentions that it "was completed and opened on 4th May
1885 at a cost of £42,614 being £8386 for lands, easements and compensations
and £34,228 for works. The length of the subway was 22 chains so that the
total cost worked out at the rate of £154,960 per mile."

He later mentions under the heading "District Railway Act 1906", "Also an
extension of the South Kensington subway from its existing terminus
immediately south of Imperial Institute Road to the northwest corner of the
courtyard of the Royal Albert Hall. This was never carried out and the
powers have expired."

Given that the subway is at a much higher level than the railway it is
unlikely that it was ever intended to be anything other than a footway.