Deep under Tower Bridge lies a vast cathedral sized space that almost seems larger than it can be, and during the winter months, the public can go inside for a look.

This is one of two large bascule chambers and is basically where the heavy counterweight swings into when the bridge opens to let boats pᴀss through. But not when you’re standing in it — and that’s why tours take place during the winter, when fewer boats ply the Thames.

Tower Bridge offers these two-hour tours, which include the areas seen by the public on a normal tour, but with your own guide taking you around and then, halfway through, a detour into a room not visited by the public.

Firstly, into one of two control cabins. While one is modern and controls everything, this one has been retained in its original Victorian design and was in use right up to the 1970s.

And yes, those are railway signal levers used to control the mechanism, and yes, there is a proper railway signalling interlock mechanism underneath, although you don’t get to see that bit.

What you do see, though, is the basement where the modern engines sit next to their Victorian predecessors.

The tour guide will compare that huge box with this new tiny widget that does the same job or explain how that small ʙuттon has replaced that huge lever, and so on.

But you’re here to see the bascule chamber, and so it’s time to go down, deep down, below the river level.

First past the large large space where old hydraulic accumulators are still in situ.

Then through a narrow corridor

And finally, and you won’t be able to avoid a bit of a wow when you walk into the chamber.

After some time in the chamber and back up to the daylight again, the tour finishes with the rest of the public areas inside the old steam engine rooms to see those in action.

The tours last about 2 hours and are available most weekends from November through March.

Tickets cost £75 per adult and are on sale now from here.

SORRY – ALL SOLD OUT NOW

A tip when visiting – wear layers as it’s cold and damp down in the chamber – and most certainly wear solid shoes with good soles to walk over the damp bricks and on the stairs.