Void Portal

The Void Portal is used to enter the Void Fields. It's found in the Bazaar Between Time. To access the Void Portal, you will need to be a character with good mobility (e.g. Loader, Huntress) or the ability to fly (e.g. Artificer). Another option is to gather multiple Hoopoo Feathers (2 should work, but the more the better).

Next, you will need to jump off the northeast (diagonal right and ahead) side of the area where you spawn in the Bazaar. As Artificer, constantly use short bursts of your ENV Suit to control your descent (space/A). As Loader, charge up Charged Gauntlet while falling (shift/LB). As Huntress, get ready to Blink (shift/LB). As any other character, occasionally jump (but make sure to save one for the final part).

You should soon see a cave opening filled with yellow light and fog. As Artificer, hold down your ENV Suit and gradually head toward it, landing inside. As Loader, release your Charged Gauntlet to fly into the cave. As Huntress, use Blink about midway past the cave. Any sooner and you’ll take fall damage, any later and you might miss, meaning you have to do it all over again. As any other character, use your last Hoopoo Feather to land on the lip of the cave.

You may not see the Void Portal at first, but it should pop into existence in the middle of the cave as you near it.