Mario next to the Koopa Bros. Fortress
Koopa Bros. Fortress is a fortress that was once home to Bob-ombs but was taken over by the Koopa Bros. prior to the events of Paper Mario. The Koopa Bros. first traveled here in search of excitement, finding their native home of Koopa Village too boring. They were apparently well-received by the fortress's Bob-omb inhabitants at first, although Kammy Koopa's admiration of them corrupted them into the vain and evil characters players are familiar with and even made them turn up against the Bob-ombs, enslaving them. Mario, Goombario, and Kooper travel here from Pleasant Path to find the first Star Spirit, solving several puzzles and fighting enemies such as Koopa Troopas, Paratroopas, and Bob-ombs. On the way, one of the Koopa Bros. traps them in a cell, where they meet Bombette (as well as several other imprisoned Bob-ombs who had previously risen up against the Koopa Bros.), who makes an escape route by exploding. They reach the Koopa Bros., defeat them, and rescue Eldstar, the first Star Spirit.
Koopa Bros. Fortress can actually be thought of as somewhat mysterious, as very little of the large amounts of information about its history given in its Tattles and other parts of the game are specific. It is, for instance, unknown who built Koopa Bros. Fortress, a fact that Goombario himself even points out in a Tattle. According to Goombario, Koopa Bros. Fortress was first erected around the same time that Bob-ombs began inhabiting Pleasant Path (which was said earlier in Paper Mario to have been not long before the game's setting), and that the Bob-ombs soon became its caretakers, although it was confirmed that they themselves did not build it. The fortress was also said to be in ruin (perhaps due to the excessive explosions caused by the fortress's Bob-omb inhabitants, something Goombario later cited as the reason for the several cracks in Koopa Bros. Fortress's walls), although the Koopa Bros. seemed to have rebuilt it upon their arrival.
In volume 26 of Super Mario-Kun, Mario and his partners encounter the fortress later in the story compared to the games.
 Enemies found
 Area Tattles
- If we continue along the pass, we should reach Koopa Bros. Fortress. Many Koopas and Paratroopas live around here. If they're loyal to Bowser, they'll definitely attack us.
- Just east of here, we can see Koopa Bros. Fortress. Actually, we're probably already on fortress grounds. That arch certainly looks like part of it. And there are lots of bad guys, too.
- Here's Koopa Bros. Fortress. This used to be ruined, but I guess the Koopa Bros. rebuilt it. It looks pretty huge, huh? And solid, too. This fortress was originally built around the same time the Bob-ombs took up residence on Pleasant Path.
- It's pretty chilly inside this fortress, isn't it? It must because there's so much water inside.
- This fortress stays cool all the time because it's built entirely of stone.
- This seems to be the central area of the fortress. This area looks extremely suspicious to me. I wonder what all those gates guard, don't you, Mario?
- I heard there are many tricky parts of this castle. I wonder who built it. It's pretty curious looking.
- It looks like they turned this large chamber into a prison cell.
- It seems strange to keep so much water in the building. Do you think it's here to keep Bob-ombs from burning the place down? Or maybe it's just for Koopas to bathe in. I mean, it's nice that it keeps the place so cool, but I'm still suspicious... Mario... Let's keep moving, huh?
- These fire bars are a menace! They're hot to the touch. They'll hurt you if you touch 'em. Somebody said there's a way to destroy 'em. How do you think we do that?
- This place is pretty huge. Before the Koopa Bros. came here, this place used to be filled with Bob-ombs. I don't think the Bob-ombs built it, but they became its caretakers. Of course, they explode all the time, so you can see why there are so many cracked walls.
- Boy, the air is refreshing up here, huh? And look at the view! Isn't that Pleasant Path way down there?
- This is the room where we fought the Koopa Bros. Those guys weren't so tough! They certainly weren't a match for us, huh, Mario?
 Names in other languages
Nokoburosu no Toride
|Koopa Bros. Fortress
||Fortaleza Hnos. Koopa
||Koopa Bros. Fortress
||Forteresse frères Koopa
||Koopa Bros. Fortress
||Festung der Koopa-Brüder
||Fortress of the Koopa Bros.
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- In the demo movie on the title screen, Mario and Parakarry are shown avoiding the Bullet Bills fired from the Bill Blasters, which only appear prior to the fight with the Koopa Bros. However, this cannot be done in-game, as Parakarry doesn't join Mario's party until after the Koopa Bros. have been defeated.