It has to have a St. Andrews Cross, even better if it has substantial ceiling fixtures for stretched bindings and/or suspensions.
A spanking horse, adjustable both for multiple sized of submissives... and for multiple heights of dominants, because yes, at some point, while bound on the horse, the submissive is going to be used, all three orifices.
A panalopy of whips and beating implements of course. The bigger the variety, the better.
A massage table so she can soothe my tired muscles after her beatings. Also good for bending her over for another round.
A shower is nice, I like to be cleaned up afterward. Big with hoses and attachments if I'm inclined toward assisting in her clean-up...
Perhaps a spa and/or sauna.
And a cool down area for my aftercare, while I watch the next set of doms use their toys.