Lumen

The planet Lumen is a world orbiting the star Sirius and home to a race of peaceful explorers called the Luminars. It is an outlandish place, devoid of atmospheric oxygen and unbearably hot for humans, except during the night, which lasts for six Earth hours.

Lumen's surface is covered by huge crystalline growths and all its native life forms (both sapient and non-sapient) are silicon-based, luminous and usually float in mid-air.

The most dangerous region (for its native inhabitants at least) is known as the Cave of Death: a subterranean complex populated by plant-like life forms which possess transparent bubble-like blisters. Despite living in a cave, these plants are still able to grow using radiation emitted by Sirius. They produce oxygen (presumably from underground water) and store it within their blisters, which can spontaneously burst at any time. This is why they are considered hazardous by the native Luminars, for whom free oxygen is lethal.