AMAZING. Museum full of vintage/replica models (including the first ever Marshall amp!), a theatre to test out everything (including two prototypes that I can't talk about except to say HOLY COW) and a chance to see the factory floor, woodshop, hand-wiring bay and finishing plant/testing rooms.
Best day ever. Totally converted back to Marshall after 10 years of meh-ing about them. 11/10 day - coz it's one more, innit ;-)