Free but should be pre-booked via YouFirst as there are only three of them.
They're not worth getting overly excited about - basically a little private room with its own shower/WC - which makes it easy to freshen up whenever you feel like it - and a daybed/chaise thingy, desk with chair, TV, telephone, etc.
Indulgent luxury it's not, but it does the trick as a private place to rest on your own, freshen up in private, or get some work done in peace.