This area is NOT to be confused to the Boulder Cave and/or Lava Trail.
The Lava Cavern, also known as the Volcano Cavern, or Impossible Cavern, is a geographical anomaly and tunneling system found in the Volcano.
It's basically impossible to get to the end without hacks. If touched with lots of health, it will still 1 hit kill.
The Lava Cavern has the same design with the whole Volcano, except for a large number of red particles it releases and the rock wall enclosing it. As the Volcano is difficult as it is, this cavern holds more danger compared to the obstacle. It mostly consists of deadly lava and is still a health-depleting zone.
The Lava Cavern can be accessed by going into the Volcano, going down the irregular path near the mid-point of the Volcano, and going into the dark tunnel leading to the cavern.