So I was mining today (Over 7000 blocks out now from spawn) And we ran into this. Have you guys ever seen something like this?
That's a fantastic cave/cavern, looks like an arena of lava. While X-ray is not permitted, many mods let you control your light level, to always have it a little brighter then usual. Spoutcraft let's you turn off night completely, so even at night it looks like mobs are walking around in the day, although I don't think it will light up caves though, but I could be wrong.
That is an amazing cave. Never seen something like that in my entire time playing Minecraft since Beta1.6.6