[PyrosNine]

Pyros' Minecraft Pro-tip:

Whenever you build tunnels or caves, dig 2 blocks deep in the ceiling, floor, or walls, and place a spongeblock (looks like cheese to me) there, and then cover it up with a block that matches the rest of the wall. This hides the spongeblock, allowing your caves and tunnels to look cool without sponges, and keeps griefers from just waltzing through and deleting all your spongeblocks.

If you make a habit of doing this for every new tunnel made, for every few feet of tunnel, then unless someone just rips the underground a new one,fills the rest of the world with water, then your creations should be fine. Even if someone rips the underground a new one, your tunnels should still be water proof to the point that repair is just a matter of walking through and sealing one or two holes and draining the water out of a few portals of water between dry spots.

Minecraft Fun tip: Watervators:
For those of us without developers tools, moving upwards is a difficult proposition, unless we're in water, or less pleasantly, lava. Scaling heights, especially from the lower cave levels, proves tricky and somewhat tedious, especially if we accidentally fall back down again, or set our spawn underground.

However, due to sponge blocks making it quite possible for water to defy gravity, a vertical shaft of water can be created that exits out into your dry, secret underwater base, making exit and entry a matter of floating upwards to the surface. For kudos, you should make a nearby second tunnel of normal atmosphere (air!) for fast downwards movement, making essentially, turbolifts: one down, one up.