Terrace

From the Super Mario Wiki

Inside the Terrace.

Outside of the Terrace

The Terrace is a Dome in Super Mario Galaxy. It is the first Dome that Mario has access to, and is unlocked once the Grand Star from the Gateway Galaxy is recovered. The Terrace's exterior resembles an Earth-like atmosphere; it is grassy and sits on a plain-like patch of the Comet Observatory.

Inside, the Terrace has starry wallpaper with a castle design in silhouette. It is the most realistic observatory in the game, due to it not having a clear theme (such as Kitchen, Bedroom, etc.) and featuring an inside that looks like a real observation room would look like in the Mario series. There is a small telescope in the corner, presumably for looking at Galaxies. As with all Domes, the Terrace has a Pull Star in the center used to access its Galaxies.

The main boss of the Terrace is Megaleg.

The Areas of Super Mario Galaxy
Domes
Terrace \| Fountain \| Kitchen \| Bedroom \| Engine Room \| Garden
Other Areas
Comet Observatory \| Garage \| Library \| Trial Galaxies \| Gate
Other Galaxies
Bowser's Galaxy Reactor \| Grand Finale Galaxy