You should save outside Gurgu Volcano, because there are a number of dangerous monsters within that can take out your party with surprising speed. The good news is that you won't find any Undead here, and not much in the way of status ailments either. What you will find is a lot of Fire, so be ready to cast AFIR and as many Cold spells as you have slots for. HEAL spells are useful here because so many creatures have Fire-based attacks that hit everyone in the party. Even LIT2 can be useful in a pinch.
Gurgu Volcano introduces a new terrain feature that is surprisingly useful: lava. Each step on a square filled with lava will result in all four Light Warriors taking 1 HP of damage, but you will never see a random encounter on these squares. The damage can't finish you off, but entering battle with 1 HP is a good way to get yourself killed, especially here. Still, on balance you're probably better off walking on lava than on normal floors, given the choice. This is especially true if you're trying to escape from the dungeon.
Gurgu Volcano B1
The first floor of Gurgu Volcano is apparently the central crater. This floor mostly serves to introduce the lava floors, but you'll also find some nasty encounters here. There are four branches spiraling from the center, and you begin in the northeastern quadrant. The stairs down to B2 are to the northwest.
Your biggest concern, here and elsewhere, is large groups of R.GOYLES. These guys look like and are statistically similar to GARGOYLES with very high Absorb, and one other very important difference: they cast spells, starting with FIR2. There is a 50% chance each R.GOYLE will use FIR2 in the very first round, and as many as five can appear at once. You can easily be taking upwards of 200 damage per character before you can even react, if luck isn't on your side. AFIR and MUTE are still your best defenses in the first round. R.GOYLES have no elemental weaknesses, either (in fact, they resist Cold as well as Fire). LIT2 is somewhat effective, and LIT3 much more so if you have it. The only good news is that you will only find R.GOYLES on the top two levels of this dungeon.
R.GOYLES aren't the only threat here. You'll run into SPHINXES on this floor, but not below. They are just as hard to hit and therefore annoying to kill as they were as a treasure guardian in the Earth Cave. The WzOGRE/GrOGRE/HYENA combination that also served as treasure guardians are here as well. Once again, WzOGRES should be considered your primary target, whether for attack or MUTE.
You've seen the other monsters on this floor before. BULLS and SCORPIONS should be old hat by now, but PEDES are still dangerous in large numbers. The rare encounter here is a throwback to the Marsh Cave: groups of MUCKS. They still hit hard, and appear in large numbers, but they will go down quickly to a physical assault.
Gurgu Volcano B2
B2 is an interesting floor like none you've seen before. You'll find yourself in a long hallway filled with quite a bit of lava. You start on the east side, and the stairs down to B3 are at the west end. Indeed, if you just want to pursue KARY, you can freely walk right across and do so.
However, the rest of the floor, a giant room with four different entrances from the hallway, is of particular interest. You'll find 18 treasure boxes here, including a full dozen in a single treasure room. However, this room is set up like a maze, and there are a variety of encounter points with nasty guards to watch out for. It pays to spend time collecting all the treasures here, then leave and save, or perhaps even return to Crescent Lake to sell your spoils before continuing your quest.
Because this floor is sprawling, you're liable to have many encounters here. R.GOYLES remain a dangerous (and common) encounter, but now you'll need to worry about the rarer battle with a group of PERILISKS. These monsters usually attack for minor damage, but they have a KO ability called SQUINT that is a serious danger to the party. KO is draining to recover from even if you have a Wh.MAGE with the LIFE spell. With only 44 HP, LIT2 should take out a group of PERILISKS despite the lack of a Lightning weakness. This is a good use for any level 3 spell slots you still have. Don't hesitate to use ICE2 if you have to, though.
The other new encounter of particular note is with the R.HYDRA. They are similar to normal HYDRAS (weaker, in fact), but spend half their turns using a nasty CREMATE attack that will drain your healing resources very quickly. AFIR is not a bad idea, but the best defense in this case is a good offense augmented with ICE.
If you want to collect all the treasures efficiently, ignore the door near the stairs back to B1. Instead, start with the second door, which leads to a room where you'll find 1,520 G. The western approach to this chest is guarded by a FIRE, a nasty creature similar to the EARTHS you fought in the Earth Cave. (You can safely approach the chest from the south.) FIRES don't deal quite as much damage as EARTHS, but you may run into pairs of them, and they have slightly better Evade. They act as guardians in several other locations on this floor, and are a rare encounter in much of Gurgu Volcano as well. Save your ICE2 on larger groups with less Magic Defense and HP, and assult solo FIRES physically.
From this first chest, head north into the zig-zagging hallway. There you'll find a Silver Helmet. The square just south of the treasure box features more FIRE guardians. Head in either direction (west is preferable to avoid the FIRES) and loop around north to a series of vertical halls.
You'll find the Giant Sword at the end of the western set of halls, guarded by an unavoidable FIRE encounter. The Giant Sword is not spectacular, but it's the most accurate weapon you've yet found for FIGHTERS or RedMAGES, so it's probably worth the effort to retrieve it. The eastern set of halls lead to an unguarded treasure box containing 4,150 G. Beyond that, you can follow the hallway north and then west to the second half of the area. If you're growing weak, now is a good time to retreat and regroup, because you can get to the next area nearly as quickly through the third door in the southern hallway on a return trip.
The last pair of chests outside the main treasure room are found in another set of hallways in the northwest part of this area. From the north, take the western of the two hallways leading south to reach them. You'll find a measly 1,545 G between the two of them, not to mention a FIRE encounter point south of the eastern chest. It's possible to avoid it and still get both chests by going around the long way to collect the second chest, but it's really not worth the effort. Either ignore these chests entirely, or be prepared for a battle against FIRE.
From the last pair of chests, head west and south to reach the treasure room. You can also reach it from the third door in the southern hallway by hugging the western wall as you follow it north, west, and then back south. The entrance to the treasure room is two squares wide, but the eastern square contains a FIRE encounter. Swing wide when entering the room to avoid it.
There is no single item of note in the room, but you'll find plenty of gold and a few other items. There is one unavoidable encounter with a Grey W, in the little nook in the middle of six chests. You'll need to defeat this foe to collect the 1,455 G in the eastern chest.
Once you're done here, you don't ever need to enter this room again. Note that the fourth door in the southern hallway leads to a long looping hallway with no treasure.