Or Wroxeter! fantasic place that we stumbled upon this summer. There's also the Kalkriese with a very interesting museum about Varus and the great Roman defeat.
Or in the above site, click in gallery, then in video clips, and make a virtual walk through old city of Rome, Coliseum, Roman Forum and Basilica Maxentius, completely free of Italian traffic!
Silchester is a Roman walled town in Berkshire...minus the houses, its just open space within the walls. Or several of the Saxon forts on the shore are still standing, some partially incorporated into later developments.
Plus a few mosaic floors here and there and not forgetting Roman Bath and the hot springs (some original lead plumbing in place). I think York still has some functioning Roman main drains.
Now when you called out a Roman plumber you really did get a job that would last nearly 2000years!
Their concrete has stood the test of time also.
Incidentally, the mosaic floors would be factory prefabricated for simple site installation....
Interestingly, I believe these mosaics were often prefabricated i.e. the tiles were stuck onto a sheet of fabric, shipped to site and then laid in one piece, unrolled or whatever and cemented in place.