The Tengchong area contains around 97 volcanic cones of various sizes, and the Mazhan volcano group to the north of the city is the most visited. The main accessible crater, Mazhan, has a path to the rim that takes about 30 minutes from the base. The interior of the crater is densely forested — the last eruption was centuries ago and vegetation has completely colonised the interior — giving the climb a slightly surreal quality: you walk through subtropical trees to reach the lip of a volcanic cone and look down into a bowl of green.
Lava field formations are visible at several points around the cone group, and the road connecting the main viewpoints passes through distinctive lava-cooled terrain with basalt rocks breaking through the thin soil. The area is best combined with the Rehai hot springs on the same day, since both relate to the same underlying geology. Maps of the volcanic field are available at the Tengchong Museum, and the exhibits there give useful geological context before you head out.