Volcán Masaya is one of the most accessible active volcanoes in the Americas — a paved road runs right to the crater rim of Santiago, where you can look directly down into the active lava lake below. On a good day (or night), the orange glow of the molten rock is clearly visible, along with plumes of sulphur dioxide rising from the vents. Evening visits are the most dramatic.
The national park covers two volcanoes and several craters across about 54 square kilometres. The active crater is Santiago, which has erupted several times in recent years and occasionally closes for safety reasons — check current conditions before visiting. The park also has a lava tunnel (Tzinaconostoc) that can be walked with a torch; it is 800 metres long and home to a colony of Pacific parakeets that nest in the crater walls.
The park entrance is about 8 km north of Masaya city, accessible by bus or taxi from both Masaya and Managua. Self-driving allows you to time arrival for sunset. Rangers lead short guided walks and the visitor centre has good background on the volcano's geology and the park's ecology.