Yes, it is a pay area and yes, there are shady places to sit all over the ship...including the pools. Some ships even have a covered pool.
The Sanctuary is adults only. Very peaceful. Choose a lounger when you book. Cost is: $20 for half day (AM or PM), $40 for all day and $30/day for the full cruise. Those prices are per person.
The AM session includes breakfast type snacks with coffee, tea, etc. The PM session includes afternoon tea. There's also a lunch menu that's extra charge (I think, never done it).
Some love it, some don't. I'm in the "don't" camp.