The Underholes

We have a central heating leak somewhere.  This is indicated by the pressure in the pressurized system slowly fading away.

We have more than the usual number of isolating valves in the system - probably resulting from past leaks and repairs - which does make it fairly simple to turn some sections on and off.  Eventually found the set that proves in which section the leak is, and yes, it's under the newly laid floor.

Most of that room has the basement underneath, but not the bit that has the leak in.

So, phase one is to clear half the basement so we can at least investigate the underfloor space that lies beyond this wall - by cutting out increasingly large sections of the ceiling; but that's tomorrow's entertainment.

Immediately beyond this wall in an inaccessible void approximately 3ft deep.  Unsure if it's some remnant of a tunnel access (which we've seen the like in houses of a similar age) or some big-scale Victorian 'drywalling' when the tower was built at this position.

There are a few 'windows' into this space. Indeed, one (not this one) looks very much like a large window surround, potentially for getting some daylight into the basement.