Mt. Lavalava

Mt. Lavalava is a volcano on Lavalava Island in Paper Mario. As the main part of the chapter, it is where Mario and his team find the fifth Star Spirit, Misstar. It is also the home of the vile Lava Piranha, whom Mario and his friends must defeat to free Misstar. The Ultra Hammer is found here. Kolorado accompanies Mario through most of the volcano, but he's not interested in searching for a Star Spirit; rather, he just wants to follow Mario to get the treasure hidden in the volcano containing a Volcano Vase. The music inside Mt. Lavalava is an arrangement of the underground theme from Super Mario World.

History
According to the Brown Yoshi in Yoshi's Village, Mt. Lavalava once erupted when the Village Leader and he were kids.

Between Chapters 4 and 5 of Paper Mario, Mario learns from Twink (who learns from Gourmet Guy when accompanying Princess Peach) that a Star Spirit is being held in Mt. Lavalava of Lavalava Island and seeks to go there. In the meanwhile, he finds Kolorado by the Toad Town port, who is also hoping to travel there in order to find a legendary treasure. The two eventually travel to Lavalava Island with the help of the Whale.

In Chapter 5, the two initially see the entrance of Mt. Lavalava, but are blocked by a lava pit. After a series of events, Mario and Kolorado make their way to Mt. Lavalava with some ropeways built by Raphael's Ravens. Upon their entrance, Mario is identified by a Putrid Piranha who then shouts "ALERT" and "REPORT TO BOSS". As the two proceed, Mario does most of the exploration, clearing metal blocks with the Ultra Hammer found inside the volcano, while Kolorado suffers various injuries while trying to be useful and even leads Mario to the wrong way at a spot. Deep in the volcano, Mario is identified by another Piranha Plant as searching for the Star Spirit, and encounters Lava Piranha, the chapter boss. Mario defeats it, and saves Misstar. This marks the end of Chapter 5.

At the same time, however, the volcano begins to erupt and their way back to the entrance is blocked by a lava-filled gap. Near the caldera, Misstar finds a cracked wall and Mario blows it up with Bombette. At the moment of life and death, Kolorado is still reaching for a treasure, while Misstar quickly carries Mario, his partner, and Kolorado and flies upward through the caldera. Eventually the four escape the volcano narrowly, and the treasure chest containing the treasure is blown out of the mountain and falls in Jade Jungle. Kolorado, chastised by Misstar for not valuing his life, eventually gets the treasure from Mario and proclaims the adventure a "complete success", a "stupendous expedition" which will be "forever recorded in the history of archaeology".

The Village Leader of Yoshi's Village states that Mt. Lavalava erupted because of Bowser's men at work. Later in the game, there is a piece of news covering the eruption, which says the same thing but cites Kolorado. Mario also receives a letter from the Yoshi kids in Yoshi's Village, which says that Mt. Lavalava stopped erupting and invites Mario to the village.

Enemies found

 * For enemy formations in Mt. Lavalava, see here.

Items found
In addition to the items listed below, two Star Pieces can be obtained from Kolorado here.

Area Tattles

 * ''This is definitely the entrance to the volcano. What do you say we explore deeper inside? The scenery around here is unlike anything I've ever seen. I wish we had time to inspect it!
 * ''Now that...is a lot of lava. Did you know it'd be this hot? And we have to cross here, don't we? I knew it.
 * ''This is a big cavern. I've heard that some volcanoes have caverns that go down for miles and miles!
 * ''These Fire Bars are a huge pain, aren't they, Mario? We can get by 'em. Don't worry.
 * ''This is a steep slope. We have to press on, but I'm getting a little tired going over over [sic] such rough road.
 * ''You know, if it weren't for that lava, it'd be dark in here.
 * ''Boy, this lava is everywhere! How are we gonna cross it?
 * ''Boy, we're real spelunkers, aren't we? My Goompa told me that means cave-explorer. Kind of like Kolorado! I wonder how he manages, exploring all by himself? At least we have each other.
 * ''This is a pit if I ever saw one. It's a big one, too. If we're not careful, we could get lost.
 * ''This is a really steep slope. If we dropped something here, gravity would make it roll down.
 * ''It's like a sea filled with lava. Welcome to the Lava Sea! Wanna swim? I'm just joking, Mario.
 * ''We need to go east from here. It's a good thing that it's just light enough to see.
 * ''This cavern is lit by the lava below, so the upper level is slightly darker.
 * ''It's hot, hot, scorching hot! It's like being slowly cooked from the bottom up! In hot grease! On a hot day! I can't take it anymore!
 * ''This place is shaking itself to pieces! This is not good!
 * ''The lava's overflowing... We're never gonna make it! What are we gonna do?
 * ''Lava has filled in the floor down there, so we can't go back down. Too bad! Well, I guess we should be moving on--with any luck to someplace a lot cooler!

In-game map description

 * ''This huge volcano rises from Lavalava Island. Kolorado claims there's a treasure somewhere inside.
 * ''This huge volcano rises from Lavalava Island. There was once a huge eruption, but it's calm now. A Star Spirit was held here by Lava Piranha.