Sachsaywaman is an archaeological site rather than a museum as such.
It is only about 2km from Cusco but the road is STEEP and taxis are cheap. It's a most impressive site with three levels of walls.
One area at the top is private access and reseach is ongoing there. It contains the perfectly round remains [foundations] of what may well have been a watchtower.
NOT ADVISED AFTER DARK.
Included in the Cusco Tourist Ticket.