The shape of Nisyros is like that of a truncated cone, with a base diameter of 8 kilometers. The centre of the island is dominated by a prominent, circular explosive crucible: the caldera of Nisyros.

With a diameter of approximately 4 kilometers, its rim ranges in altitude from 250 to 600 metres, while its floor is 100 metres above the sea level.

The west-north-western section of this basin is occupied by the hills of Boriatiko, Visternia, Nifios, Profitis Ilias and Trapezina.

Nisyros is a complex stratovolcano, initially created at the bottom of the local sea. The continuous eruptions and pouring of lava resulted in the emergence of volcanic rock above the sea level and the creation of a most scenic island.

The island is part of the recent active volcanic arc of the South Aegean Sea and constitutes one of its youngest parts; this is attributed to the very well preserved geological formations as well as to an impressive thermal anomaly, manifesting itself on the surface (fumaroles, hot springs, craters etc). The variety and simplicity of volcanic structures allows them to become understood even by non-experts: an impressive caldera, four km in diameter, large volcanic domes, lava necks, impressive lava flows outflowing to the sea, pyroclastic products (pumice, scoriae), surge deposits of volcanic ash, mixed magma, dome collapse breccias, hydrothermally altered formations and much more, create a scientifically and visually interesting landscape of terrain, colors and formations.

Only for the above reasons, Nisyros could potentially attract more visitors and assist all concerned parties in understanding the volcano genesis and development processes.