John Rowland wrote:
There is an obelisk in Circus Place with ventilation slots near the
top. Just to the south is a huge drain big enough to lower a van. Any
clues?

Yes, I have often wondered about this.
Presumably it is some sort of access shaft.
Possibly an elecricity substation or similar?
http://www.flashearth.com/?lat=51.51...20&r=0&src=msa