The island is known for the Broch of Mousa, an Iron Age round tower, and is designated as a Special Protection Area for storm-petrel breeding colonies.

Geologically beds of hard sandstone alternate with muddy limestones that weather to produce fertile soil.

Mousa's fertile soil supports a rich diversity of plants, including sheep's-bit and creeping willow in the herb-rich grassland, despite the wind, salt spray and grazing by sheep.

[11] The seas surrounding the island host a population of sandeel that provides a food source for many species of fish, seabirds, seals, whales and dolphins: the area is considered to have the most reliable population of sandeels of all the seas surrounding Shetland.

[15] The 2000-year-old round tower stands above a rocky shoreline, one of a pair of brochs guarding Mousa Sound.

The entrance passage into Mousa Broch is long, reflecting the enormous thickness of its walls.

[19] The island is readily accessed using the passenger-only ferry which operates from the Shetland Mainland at Leebitton, Sandwick in summer time.