Literally: heavens – up – heavens – down
Alternately: The world above the sky (the heavens) and the world below the sky (the earth). Also, the space between heaven and earth. The whole world.
Notes: Reading 下 as ge instead of ka is somewhat unusual; this use of the “Wu sound” marks the phrase’s antiquity and ties in with its Buddhist origins.
This phrase apparently sees less usage on its own than its partner 唯我独尊, or compounds with comparable meanings like 有象無象 or 森羅万象, but it sure did get made into a manga about… supernatural punching, I think? And swords and stuff.