The National Museum of Computing (just up the road from Bletchley Park) has a working Colossus

I don't think I would describe the NMC as "just up the road". It's the same physical site.

If you consider the NMC "just up the road" then the Bletchley Park site you're thinking of is also "jump up the road" from er, Bletchley Park, a stately home that's less interesting to a nerd than either the NMC or Bletchley Park museum about war era "intelligence" but might be fascinating if period furniture is more interesting to you than the world's first (for many different values of first, the museum has several options, but not all of them) programmable computer.

the nmc is most interesting, but also pretty cool to see turing's office in hut 8 (i guess the portable classroom like structure for a computer lab is a trope that goes all the way back to the beginning)!

that's what i was describing! :) it's on the bletchley site (they share a parking lot) and was where tony sale and friends rebuilt the colossus.

although i just looked. critically they have different ticket offices. it was a long time ago! either way, worth a visit of both and they make up an excellent way to spend a day.

It's on the same site but there is some institutional nonsense that means getting onto the Bletchley site doesn't guarantee access to the NMoC, which is only open on Tuesday, Thursday, Saturday and Sunday.

Don't ask me how I know...