I leveled up 4 of my 6 characters to level 7. Indeed, that did grant my cleric 4th level magic, which includes the ability to heal poison (and some other status ailments; one spell I haven't used yet is "Rise").

It didn't take too long; it took about an hour for my first character to level up, and an additional half hour for the last one. I did all the level building in Sorpigal. Most of the "set" battle locations now have reasonably powerful monsters (the exception, oddly, is the first few battles in the Jail). I had to fight virtually all set encounters to get the necessary experience. It seems as though so long as you don't die, leave the area, or reset the NES, set monsters will not recover (it seemed that way to me before, but I never had gone so long without getting a game over before).

After I had all the experience I needed, though, I got in several random encounters in a row. I ran from some of them.

My other two characters need ~15,000 experience to level up, so I won't even worry about them for now.

Now that I'm a little stronger, I have three things I could try wrapping up: The North Barrier (which I'll probably attempt first), finish mapping C2, and fighting the statues at the west edge of C2.

After I'm done with that stuff, I'll probably be free to explore.

"Any life when viewed from the inside is simply a series of defeats."
-Orwell