Disorienting, treacherous, vast, and grand on a scale that almost all other levels have been unable to accomplish. This was one of the first major breakthroughs in two-player gameplay during 1.9, though that isn't even the main focus here- it's about the journey you take through the titular cave that makes this level as good as it is. I do not remember who said this, but I recall someone saying that this was the first bossfight in GD, and they were absolutely cooking here- it is great to think of the Horntail Dragon itself as the one arranging this challenge, as you see it lurking throughout the level, keeping a careful eye over you, before throwing down the gauntlet and casting the player into two equal halves, a final test of will and courage before you slay the beast and escape its dreaded lair. Do you have what it takes to confront it (as well as a part of yourself)?

Overall, the GD equivalent of Linsanity- KeiAs literally has not made a better level before or after, it's just this much of a phenomenon.