I'm playing through an adventure map and I found a large dark cavern I must traverse, but there are just too many mobs (I'm not kidding, there's an insane amount of mobs). I ended up having to wall myself into a corner.
Ordinarily I would wait until morning and walk through it/light it up then, but no sunlight ever reaches it.
What's the safest way to light up a cavern?
Bit by bit, if necessary block by block. I'm not kidding, that's how I'm taking dungeons.
When in doubt, a bucket of lava (from a high and safe spot) solves everything.
One way to keep a lot of mobs at bay is to dump a few buckets of water. Be careful not to get yourself on the wrong side of the water flow, and make sure you cover the left side well since mobs tend to move to your left.
You can then pick off the creepers and skeletons with a bow, and the rest should be easy to kill with your sword since they can't fight the current. Don't forget a full set of iron armor. It really, really helps in 1.0.
Of course, you didn't specify what resources you have available to you in this adventure map, so your mileage may vary.
Depending on how deep you are, it may be an idea to dig a shaft to the surface - the added bonus of this being that when the sun rises, those mobs at the bottom will need to be wearing factor 40,000 or they're going to have a pretty bad day.
It's not safe to dig directly up, so dig a 2x1 (or bigger) shaft very carefully and build up dirt underneath you, making sure there is a hole in front of you, directly under the blocks you are digging out - this way if you hit lava higher up it will not flow along the floor and burn you - it will flow into the hole. If you manage to reach the surface safely you can dig straight back down to where you started.
This is potentially a very slow way to solve your problem, but once you have that shaft dug, you can place a couple of signs on the wall at the bottom, then pour water on top and you have a very fast and safe way to get to the bottom of the world :)
