When Mario reaches the second Bullet Bill launcher in Tostarena Ruins, look to the right to spot a Moon on a leaning pillar.
To the right of the hill, there’s an alcove with a hidden moon. In Tostarena Ruins, look for the long ramp of sand just north of the entrance. Hit the flowers with Cappy and bounce up to the top of the dome to grab this easy Moon. Found on the dome of the blue / yellow building in the back-left corner of Tostarena Town.