The "Mouth of Hell" is a viewpoint on the southwestern crater rim, reached by a short flat trail from a small parking area off the rim road. It looks across the whole caldera — Lagoa Verde and Lagoa Azul together, and the smaller crater lakes Lagoa de Santiago and Lagoa Rasa to the south — and is widely considered the single best view in Sete Cidades, narrowly beating Vista do Rei because more of the crater is visible at once.
The walk is about ten minutes from the road, mostly level along a fern-edged ridge. Go early: the southwestern position means cloud rolls in here first, and an excellent morning view can be gone by 11 a.m. The site is also free of buses, since coaches cannot reach the parking area.