I'm not sure one's been set. There's a small entrance in the edge of the lava lake near Kos's house and a couple of ladders in the middle of the sea somewhere. Or you could use the secret staircase near the teapot.
Not the teapot near the original spawn. Which is the one I thought of originally when Kos said it had reached the teapot. That confused me a lot.
Minecart Mania is installed and seems to be working.
Mouse:
Read this: http://www.minecraftwiki.net/wiki/Mods/Minecart_Mania!
And then make an awesome underground railway inthe tunnells :D