Lac Pavin

Pavin fills a maar, a crater blasted out when rising magma met groundwater, and at roughly seven thousand years old it is the youngest volcano in mainland France. The lake is almost exactly circular, about eight hundred metres across and ninety-two metres deep, ringed by beech forest that drops straight to the shore. It is meromictic: the water below about sixty metres never mixes with the surface layer, staying without oxygen and holding dissolved gases, which has prompted research into whether it could release them suddenly as some African crater lakes have done. A level path circles the shore in about an hour.

What you actually see

• The circular crater - an almost perfectly round lake in a young maar.
• The beech ring - forest dropping directly to the water on all sides.
• The shore path - a level circuit of about an hour.
• The deep layer - water below sixty metres that never mixes or oxygenates.

When to go

May to October; autumn colour in the beech is the best time. The area is snowbound in winter and the road can be difficult. Summer weekends bring crowds from Besse.

Honest expectations

Swimming and boating are restricted to protect the lake. Parking is charged and limited at peak. There are few facilities beyond a seasonal cafe.

Nearby

Puy de Sancy lies northwest; Besse is a short drive east.