If you’re looking this up, I’m gonna go ahead and assume you’ve taken down the Thardus boss fight and grabbed the Spider Ball power up. After you head out of that area and make your way towards whatever’s next, Metroid Prime’s hint system should kick in and tell you about some temperature issues and mark a room called “Antechamber” on your map. It looks like a far away pain in the ass to find, but it’s not as bad as it looks. Here’s how to get to the Antechamber in Metroid Prime Remastered.
First, you need to make your way all the way back to the Chozo Ruins. On the way there you can find several upgrades thanks to your new Spider Ball ability, so feel free to do some backtracking around various places you’ve been before. But ultimately you need to make your way through the Chozo Ruins and get to the Main Plaza room, hop up onto one of the raised platforms and through a door into the Ruined Fountain. From there your path is the Arboretum, Gathering Hall, Energy Core, then finally the Furnace.
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From the Furnace there’s a Morph Ball tunnel that takes you to the Crossway. Use the half pipe to reach a Cordite slab, which you can blow up now that you have those Super Missiles. This will set you on a chain of events that gets you where you need to be. Scanning the gimmick behind the Cordite makes a track appear for the Spider Ball, and also opens a door to the Hall of Elders. There’s a miniboss fight here against a Chozo Ghost, then a puzzle to solve.
To solve the puzzle you need to Morph Ball in the statue’s hands, then get ready to use Spider Ball when the statue chucks you over to a track you can’t reach otherwise. Bombing a Morph Ball slot makes three more color-coded ones appear; shoot the purple one with the Wave Beam to open it up, then bomb it to gain access to the next room, the Reflecting Pool.
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In the Reflecting Pool, use Morph Ball to go into the water, and bomb the little circle in the middle. That opens up a drain, so now you can use the pool as a half pipe to bounce yourself up to a connected save room. If a frog tries to eat you, blow it up from the inside. Opposite the save room is a door (you can jump across no problem) that leads into the Antechamber, and the Ice Beam power up.