Strangely, I don't mind that so much as the probable lack of nice toilets.
We Shall See. The Fringe Festival uses this venue at least once every year, so there must be some small amenities. Also, our concert dress is going to be simply "black," i.e., my long black down coat which looks like Charlie Brown when he fell on the ice, would be appropriate. And this isn't a regular concert; it's sponsored, so we don't have to sell tickets, though encouraging people to come is always nice.
Most importantly, the acoustics are apparently mind-bogglingly excellent. Since this concert is mostly an excuse to record, so the composers will have their piece available to them, the acoustics are an important factor.
Nonetheless, I think I shall research available nice toilets in the area.