Indoor attractions suitable for 3yo?

[pearandsausage]

Posting here for traffic (sorry).

Want to go away for DH's birthday in March.

DS will be 4 in the summer so looking for something he'll enjoy to base the trip around - given that the weather could be doing almost anything I was wondering about an indoor/mostly indoor attraction (Diggerland is top of the list but is all outside). Does anyone have any recommendations?

Southern half of England preferred but will travel if it looks good!

Does he like aquariums? My preschoolers were very fond of them, especially the ones with touch pools. We'd go through the overhead tunnel things about 10 times on repeat.

I think Diggerland has a fair number of rides that have height minimums - check.

Some possibilities:
www.greenwoodfamilypark.co.uk/
(Menai area, perhaps too far)

Hire Beach hut (e.g. Southwold) and go along the pier to both the new and the vintage amusements, play mini golf etc. as well as beach in front of you. Everything very walkable from the huts. But book early.

One of our favourites was the Rail museum in York.

They always liked castles as well... but they are mostly outside!

Ah good shout @HiccupHorrendousHaddock it's been quite a while since we went to one, I think he'd love it.

He's a giant child @Ormally so ok on height restrictions

I fancy the transport museum in London @PuttingDownRoots but DH not really a city fan!