Sinus Iridum is a plain of basaltic lava that forms a northwestern extension to the Mare Imbrium on Earth's moon. It is surrounded from the northeast to the southwest by the Montes Jura range. The protruding part of the range at the southwest end is named Promontorium Heraclides, while that at the northeast end is called Promontorium Laplace. This bay and the surrounding mountains is considered one of the most beautiful features on the Moon, and is a favorite among lunar observers.