This is underselling it: it's in a side street off Newbury, where nobody would have any reason to go, with a tiny little door about half the size of all the other doors marked "Puppet Library"[1].

I visited many years ago by complete accident: I was out running with some friends on a Tuesday afternoon, we were going down the public alley because Newbury was heaving, and saw this sign. We wandered in, and...yeah, there's a lot of puppets.

[1]: https://maps.app.goo.gl/pa6sTiQ1cFsp2mqcA