Merchant Adventurer's Hall, York
This building was built in 1357 -61 and is one of the largest of its kind in Britain. "The timbered Great Hall was where merchants conducted their business and held their courts and social events. The Undercroft or hospital is where they cared for the poor." (from website)
It's quite an interesting building and the floor is very wonky, pretty much all at an angle.
The Hall is available to rent out for functions and I think it would make a pretty cool wedding hall if you so desired. Just watch the floor when you dance!
Admission is £2.
It's located between the streets named Piccadilly and Fossgate.