The cave is unique within the UK in that the first chamber has been formed by the action of the sea, whereas the inner chambers are freshwater passages, formed from rainwater dissolving the carbonate dolomites.

The cave can be thought of as two caves formed by different mechanisms that have joined together over time. The cave is composed of three main sections: a large sea cave entrance chamber, a waterfall chamber, and a short freshwater passage that leads to a terminal sump chamber with some flowstone formations at the rear.

Partway through the cave the waters of Allt Smoo also drop in as a 20 meters high waterfall. This is mainly due to the nearby dolomite–quartzite geological boundary where the Allt Smoo stream crosses the impermeable quartzites and sinks on meeting the permeable dolomites.

The cave entrance and main chamber have been considerably enlarged by sea action to approximately 40 meters wide and 15 meters high, the most significant sea cave entrance in Britain. The entrance is located at the end of a 600 meters long tidal gorge (Geodha Smoo) which was once part of the cave, now collapsed.

Several remnant pillars can be seen along the eastern side of the Geodh along with a large section of the previous roof which has been partly buried by the grassy slope (normally covered by rocks spelling out the names of visitors to the cave). The sea rarely enters the cave nowadays (only during spring tides) as the area has undergone isostatic uplift.

According to the Internet