Okutsusha is a holy place where the spiritually minded come together to pray. You can do the same, or respectfully observe others in worship.
You'll soon see why this Aisai sacred place is visited by many travelers. If you're looking for other things to see here, Kiyosu Castle, Zenkoji Temple, and Tennogawa Park are in this area as well. They won't take long to get to from Okutsusha.