A Great Victorian building, but not very accessible.
I was there for an event that includes all abilities and disabilities and I saw some folk in wheelchairs having difficulty with narrow doorways. Other commenters have mentioned access to the toile...
Accessibility depends quite heavily on whether you visit on a day which is well staffed. Some times of year you can ring intercom in vain. I was lucky, though.
Overall, difficult to get access to the building.
The access, parking and toilets altogether made it very difficult for Euan to gain access to the building.