As a semi-regular guest there, I'll toss in a vote for the spa at the Pen ^^^
Note that they're currently undergoing some renovation/construction in the usual treatment area and the check-in has been moved from the 20th floor to 19 (elevator button for 20 defaults to 19) for the duration. However, during the renovation, they are using regular guestrooms (with adjustments re removal of furniture to make room for the spa beds, etc) for treatment rooms.