LEGEND
LD = Locked Door
Up Arrow = Ladder Up
Down Arrow = Ladder Down
T = Trap
scattered dots = Poisonous Swamp
Squares and Rectangles = Mostly Bridges over water, in Lv 1 and 2 they represent buildings and hallways
This Cave can be accessed from any of the 4 corners of Lord British's Castle and from a closet in the Wayfarer Inn (as shown in the tutorial.) Wile there are a few places lower level characters should avoid, most of it is an adequate challenge to those just starting out.
On the each level there are quite a few places that a Lv 1 character can use to "funnel" monsters into an small area, doing this allows low level players and party's to take on a large group of monsters one at a time.
Level 1
The First Level here is nearly devoid of monsters save a few Giant Rats Here and there. In The Far South West Room you can find the NPC "Daros" who will give you an amusing "Rubber Ducky" if you talk to him.
NOTE: at the Marker #1 I have noted the location of a Cauldron you can take without stealing (to use in the Hot Air Balloon quest)
Level 2
for people just starting out with the ultima series just stick with the tutorial as if you start to wander this level can get kind of confusing as to where you are. mostly you will only fight giant rats and bats and such.
NOTE : At Marker #2 you will encounter a group of headless, Trolls, and a Giant. this may not be too difficult for large groups or mid level characters but for the Lv1'ers wandering about you would do well to avoid this fight if you can.
Level 3
Fallowing the Tutorial will bring you to the home of Phoenix Northwards. At level 1 it may be best to run up to the small narrow tunnel that leads to her home as to bottleneck the rats and bats into attacking you one at a time. be careful of the traps in that tunnel as you wont have vary much health to spare (traps include a poison gas field and a hidden Bear Trap) Included in the treasure chests and crates near her home are some gold nuggets, flasks of flaming oil, some wands, and an invisibility ring. Phoenix herself is a bit antisocial ... but is required for the Pirate Map quest (you have to "Pickpocket" a thieves guild belt off of her to get Homer to talk to you.
NOTES
At Marker 3 you a Skiff will spawn that you can use to get to the ladder down to Level 4.
At Marker 4 is the body of an adventurer killed by gremlins. he has a bow, some arrows, and a protection ring.
At Marker 5 is a trolls den ... at low levels (if you have the guts to do this) a single PC can make a good show of himself taking them on. the narrow tunnel that connects this cavern to the main chamber only has one way in or out. As a result you can force each one to come at you one at a time. It is an efficient way for new characters to gather equipment and gold for later adventuring. To say nothing of the experience you can gather.
At Marker 6 is a Gazer and some Headless. Lv 1 characters are (as far as I'm aware) immune to monster spells but as this fight is out in the open, it may be a little much for starting characters to take on.
Level 4
Unless your heading to the Buccaneer's Cave at the far side there is really no reason to head down to this level. serpents in the water by the ladder to Level 3 and green slime by the ladder to Buccaneer's cave.
Addendum
I have in my possession some pages from the original Origin Strategy Guide for this game. the guide was presented as a Journal written in the words of two NPC's found in the U6 world "Mandrake" and "Penumbra." The standard Text is in the words of Mandrake ... and the Italics are Penumbras additions. This part doesn't really add anything important, its just a fun bit of flavor for those interested in the story.
Lord British thought it would be a good idea to develop a system of sewers in Britain. It's getting to be a vary big city, and he wants to keep things sanitary. He didn't realize the tunnels. would turn into a breeding ground for monsters! I guess the rats and slime feed on the garbage that gets washed down there. But there's worse monsters than them. Seems the tunnels connect to a natural network of caverns that lead all the way to Buccaneer's Den, right under the sea herself! Now, I used to go down under the castle several times - whenever I needed someplace private to take the ladies who couldn't afford to be seen with me. Daros always knew when I was down there, but an occasional gold coin or two was enough to get him to mind his own business. One day, I found myself in Buccaneer's Den, with no money, no boat, and rather more to explain to a band of angry pirates than I felt prepared to deal with. I felt it prudent at the time to sneak through Buccaneer's Cave into the sewers. I hope that's not a stunt I'll have to pull again. There are trolls, bats, headless, gremlins, and cyclopses down there - even a sea serpent or two! I was lucky I found a skiff on the third level near the ladder, because I wouldn't relish the thought of swimming in the sewerwater. That skiff might still be there if you went looking. I left it by the island with the bridge leading out to it.
A lady named Phoenix lives down on the third level as well. She's a fine figure of a woman, and got a pretty nice place set up down there. A bit too aloof for my tastes, though. Perhaps it has to do with the belt I saw her wearing. "Outsiders" aren't supposed to know, but I recognize the sign of membership in the thieves guild when I see it. I left her boudoir in rather a hurry after she tried to part my hair with a dagger. It'd serve her right if you were to steal back some of those fancy things from her. She had some nice looking treasure stored out behind her house.
Anyway, by the time I got back to the part of the sewers I knew, I was so eager to get back to the surface I didn't worry too much about which ladder to take. Ended up in a closet in the Wayfarer Inn. Just my luck, it was in one of the occupied rooms. "Don't mind me," I said to the couple that was staying there, but I imagine they probably did. I didn't stick around to find out.
** You may find some potent magical item in Phoenix's treasure chests - but be wary of the traps she has placed to protect them. **