Hi there, and yes :o( there is a fee for the Sanctuary, I can't remember for certain but the figure of $15 per day comes to mind.
They do sell longer term passes as well, and I have it in mind that days in port were less than days at sea.
Having said all that, the last time we were on Grand, the "never-ending" pool below the sanctuary & it's two whirlpools were still free :o)
It was a nice quiet area albeit shaded around the pool, so the bench seating that steps up/down to is was in use for sunbathing.
Hope this helps,
Alan & Katrina
Last: Oceania Nautica Aug 2016
Next: Cruise Maritime Magellan Nov 2016
Then: P&O Oceana December 2016
Golden, Grand(2), Caribbean, Royal, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Britannia, Oceana(3), Oriana(12), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(7), QE, Caronia(2),
Oceania Nautica, Minerva, Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey