It is the Museu de la Tècnica de l'Empordà in Figueres, website http://www.mte.cat/ http://www.mte.cat/ . According to the website, only open by appointment, so

It is the Museu de la Tècnica de l'Empordà in Figueres, website http://www.mte.cat/ http://www.mte.cat/ . According to the website, only open by appointment, so he got lucky indeed that he could just randomly walk into it. The tweets make it seem like the museum is far outside the town, but it's actually just 200m outside the city centre. Figueres is easy to reach by road and both classic and high-speed rail.