Devil's Peak Walkthrough - Persona 1
Devil's Peak is an optional dungeon which you can access at any time during the Snow Queen Quest route. At first you will only be able to access the first floor of this dungeon, each time you complete one of the three main towers of the Snow Queen Quest you'll unlock additional floors for you to explore inside of this dungeon.
After beating all 3 towers you'll get access to the first 7 floors of this dungeon - to gain access to floors 8 and above you'll have to beat the game. This dungeon serves two main purposes, the first and most important purpose is you can grind EXP and Spell Cards inside of this dungeon during the Snow Queen Quest. Its second purpose is it's the only post-game content available for the Snow Queen Quest.
Unlike the SEBEC Route, the Snow Queen Quest doesn't have many opportunities for you to stop and grind EXP/Spell Cards. Each tower that you do is timed and there is no save point/health fountain inside of them - so you can't reliably stop and grind inside of them. Also, each tower has pretty significant jumps in difficulty which means you'll very likely have to do some grinding between each of them.
This is the only purpose that Devil's Peak serves until you beat the game and unlock the final floors of this dungeon. With this idea in mind, Devil's Peak contains all of the monsters that you encounter normally throughout the game. The first few floors of this dungeon are the easiest and the enemies that spawn will progressively get harder and harder as you climb up.
Below are links to the Persona 1 wiki detailing what enemies you can encounter on what floor.
With all of that out of the way, below you'll find map screenshots for every single floor in Devil's Peak. Floors 1 - 7 are your standard mazes and there isn't much unique about them; it isn't until you reach Floor 8 that things start to get interesting. As stated earlier, you won't be able to progress past Floor 7 until after completing the Snow Queen Quest and unlocking the rest of this dungeon.
Starting on Floor 8 the way this dungeon works will start to change. Now, in order to progress from one floor to the next you'll have to defeat a group of demons inside of a room on that floor. To begin the fight with these demons you'll have to interact with a stone inside each of these rooms.
You should expect these demons to be as difficult as any boss you've faced thus far - honestly they're actually harder. The demons you fight in these rooms will be beefed up versions of the same demons that you've faced throughout the game getting to this point. I think this makes the fights a little easier because you should have a rough idea of the strategy to use against these demons since you've faced them so many times before.
Aside from having to beat demons on each level to unlock the door to the next floor you'll also have to avoid many different pitfalls. Use my map screenshots for help navigating this dungeon - I did my best to mark all of the pitfalls that I could before taking the pictures.
The final floor of Devil's Peak is also going to be the most difficult (obviously). On this floor you will have to clear a total of 6 'bosses', one in each room. All of these fights work the same way as the previous ones, you will inspect a stone pillar and a fight will begin against a group of very powerful enemies.
Inside each room on this floor you will find 3 pillars, 2 of them will have fights against 6 Slimes and the third pillar will have a fight against the boss. You only need to defeat the boss but I recommend you defeat the Slimes too since they give a lot of EXP. Before you try and take on the enemies on this floor I strongly recommend you stock on restorative items because you will need them.
Sadly I am not good enough at the Persona series yet to offer you advice on how to win these difficult battles. The only real advice I can give you is that it comes down to the Personas that you are using on each of your characters. You can make each of these fights easy if you equip Personas that will resist, reflect or absorb the one-shot mechanics that the enemies throw at you.
For more information on what Personas are the best I recommend you check out my Persona 1 Best Personas Guide. Linking you to that guide is the only real advice that I can give you, sadly. Defeating all 6 bosses on the final floor of this dungeon will reward you with the Snow Conquest Badge item. This item serves no purpose what-so-ever aside from bragging rights that you completed this dungeon.