Lava Dive Room
|Lower Norfair Elevator||Adjacent rooms||Kronic Boost Room|
Historically this room has previously been called the "Gravitron", presumably because of the perception that you need Gravity Suit to get through.
It is possible to perform a shinespark from the bottom of the lava pool and reach the entrance of Lower Norfair.
First, perform a short charge while entering this room from the previous room, then crouch at the edge of the lava pool (to charge the shinespark) and fall in. Damage boost off of the first Namihe's fireball and shinespark directly up when you are above the bottom of the pool.
Due to lava's physics, a player can perform a diagonal shinespark instead of a vertical shinespark and still have the shinespark travel directly upwards. Besides having a different animation, a diagonal shinespark will carry Samus approximately five pixels right as it travels upwards. This is helpful in instances where the spark was activated later than preferred, as it will shift Samus back to the right and help ensure that the shinespark does not end below the flooring of the entrance to Lower Norfair.
Otherwise, you can just run down the stairs until you pass the third Namihe, then Space Jump up to the platform leading to the elevator.
Or you can Space Jump through the lava with a Pseudo Screw, which allows you to move through the flames without taking damage.
Running down the stairs and Pseudo Screwing through the lava appear to be about the same speed optimally, so the choice is down to individual execution.