The Palace of Shadow is the final area that Mario and his comrades visit in Paper Mario: The Thousand-Year Door, and is where the Shadow Queen resides. It is accessed by going through The Thousand-Year Door. The Palace is one quarter of the old city that was ruined 1000 years ago. Over the years during which the Queen reigned, the Palace became rich with stolen treasure, which became legendary over the centuries since her defeat.
In this palace, the Shadow Queen possesses Princess Peach, who Sir Grodus had delivered to her. Mario and company drudged through the palace and its inhabitants, including the middle sibling in the "tail" family, Gloomtail. Mario and his allies later fought with the Shadow Sirens, who now consisted of Beldam, Marilyn and Doopliss. Soon after, Mario's party finally made it to the Shadow Queen's inner sanctum, where Sir Grodus was. Mario and his party defeated him, and also defeated Bowser and Kammy Koopa, who literally "dropped in" on them unexpectedly. Sir Grodus retreats to the final room to use Princess Peach as an offering to the Shadow Queen.
The first room is rich and very detailed with roses and patterns. Past this is a bridge across an expanse of water, the cave "ceiling" can be seen here. The room afterwards is a large staircase that goes even farther underground. Later, a garden area shows off some streams and the Riddle Tower. After the tower's riddles are all completed, some ancient machinery will activate, causing the long hallway leading to Gloomtail to collapse, revealing a lower area filled with enemies. One of the last rooms is a huge chamber with odd pillars, and then, the throne room where Grodus uses Princess Peach. A secret door leads to a huge staircase down to the crypt containing the Shadow Queen.
 Enemies and Bosses
 Area Tattles
- This is the entrance to the Palace of Shadow. It's seen no visitors for 1,000 years... It's so big... It kind of overwhelms you, doesn't it? And that treasure is here... Treasure or no, I don't like the vibe from this place... Maybe it's just my nerves...
- There's a long stairway connected to this underground lake. Those lights floating in the darkness are really pretty... but also pretty spooky.
- We're inside the Palace of Shadow. There's a long corridor leading down. This palace sure is big and super-rich-looking, huh? I wonder what kind of people lived here before the place slept for 1,000 years?
- We're inside the Palace of Shadow. This is a corridor, I think... Looks like spike traps... Forget the enemies... Just take it one step at a time!
- We're inside the Palace of Shadow. There's a large bridge over the lake here. Those fire bars in the middle are kind of a problem, huh? We'd better avoid them. If you're all sketched out trying to jump them, just use Vivian's Veil ability!
- What a humongous room... I'd say it was pretty, but even this place feels weird... It's like the whole palace got cursed or something. Did you just say "duh" to me?
- We're inside the Palace of Shadow. There's a long hall leading down from here. It kinda feels like the earth is slowly swallowing us as we progress down. Yuck.
- We're inside the Palace of Shadow. There doesn't seem to be anything special here. Still, it has that same gross feeling... even though it's so nice and spacious...
- We're inside the Palace of Shadow. Seems normal... but I bet there's a secret here... We should check EVERYTHING to make sure there's nothing amiss, don'tcha think? You know... Look for anything out of the ordinary...
- This is the palace garden... but it feels so cold and icky. It's like time stopped here... We gotta do something about those Chain-Chomps in the middle if we wanna move on. Yeah, that's right... I don't just mean the moving ones...
- We're inside the Palace of Shadow. This seems to be a corridor. I'm observant, huh? Listen, Mario... I know I've said this before, but don't forget that you're not in this alone. You should rely on your partners' abilities if you ever get stuck or anything.
- This is another corridor. I wonder how long these things go on? I'm sure we'll need all of your special skills, AND those of your partners. Don't forget to use your strongest muscle, too... Your noggin! Hee hee!
- We're inside of the Palace of Shadow. This is another corridor. Big surprise. We'd better watch below our feet as well as above our heads, know what I mean? But, uh, don't forget the area above your head, too! Does that make any sense?
- We're inside the Palace of Shadow. There don't seem to be any big puzzles here. We just need to go open that door on the right. That's all. Whee. Exciting.
- This is Gloomtail's room. I wonder if he was here for all 1,000 years? Dragons do live a long time, I heard, but dang... Without him in it, there doesn't seem to be anything special about the room.
- How could there be such a huge tower underground? And why was it built...? There seem to be a lot of rooms here... and every one contains a riddle...
- There's something written on the wall. Based on that message, I'd say... That word "beyond" probably refers to away from the door. So that means the left block. So then the word "before" must refer to the right block. Are you with me, Mario? Still, the way they repeat those words must have some meaning too, don'tcha think?
- There's something written on the wall. Based on that message, I'd say... Maybe if we break a block here, it'll do something to a block in another room?
- There's something written on the wall. Based on that message, I'd say... There's something fishy about the wall here? Uh, maybe? We oughta investigate...
- There's something written on the wall. Based on that message, I'd say... ...There's definitely something in the center of the room, don'tcha think? But what are we supposed to do with something we can't see? This is insanity!
- There's something written on the wall. Based on that message, I'd say... We're supposed to defeat these guys in order, from weakest to strongest? Uh... Well, I know the weakest is the Dull Bones in the green shoes there... That help?
- There's something written on the wall. Based on that message, I'd say... I guess we just have to go straight in from the entrance. And then when we get to the wall, we have to do something... Yeah... something.
- There's something written on the wall. Based on that message, I'd say... That if we can be seen, then there won't be anything to see in this room? ...Huh?
- The gears in the back of this room started moving when we unlocked that planetarium... Listen, Mario... We're gonna have to rely on everything we've learned to get through this. Just think about what we've been through, and I'm sure you'll find a way, OK?
- We're inside the Palace of Shadow. This place is all about kooky puzzles, huh? You see those marks in the middle of the corridor? They've GOTTA be important.
- We're inside the Palace of Shadow. We must be WAY underground by now. I'm totally running out of advice at this point, sorry. I have advisor's block. Hey, but don't worry! Have faith in yourself and your friends, and we'll win!
- What is this weird room? It's quiet... A little TOO... Well, let's just say it's quiet. There's a Save Block over there, and I'm thinking it would be smart to use it.
- This must be the main hall or something. It sure is a humongous space... This must've been where the most important person in the palace stayed... But standing here makes me totally uneasy... Why is that?
- There's a long, long staircase leading down. And I get a REALLY nasty feeling about what's waiting down there. But we've come this far, so we gotta soldier on. Let's go, Mario.
- We're in the deepest room in the Palace of Shadow. ...The Shadow Queen's crypt. I gotta be honest... I totally thought we were goners at the time. Seriously. I was secretly wigging out, but then I saw how you wouldn't give up... Awesome. Anyway, enough reminiscing. There's nothing here now, Mario. Let's go back.
 Names in Other Languages
Yami no Kyūden
|Palace of Darkness (from yami 「闇」, meaning "darkness" and kyūden 「宮殿」, "palace").
||Palacio de las Sombras
||Palace of Shadows
||Palais des ténèbres
||Palace of Darkness
||Reggia delle Tenebre
||Palace of Darkness
- The main track of the palace is a remix of the Underground theme from Super Mario Bros. with some added dark, eerie sound effects. This music also briefly quotes the Castle theme from Super Mario World. The music for the second half of the palace is an even darker remix of these classic melodies.
- In many of Goombella's descriptions of the rooms of the palace, she mentions an aura that makes her feel extremely uneasy, most likely the extreme evil occupying the thousand-year old palace.
- The Palace of Shadow is the only place in the entire game without a single Shine Sprite or Star Piece.