Borderlands 3 (BL3) has 6 Eridian Proving Grounds Trials and this guide shows their locations. Finding and completing all Trials unlocks the 100 Proof trophy or achievement. They also count as side quests so they are needed to finish all side quests too.
None of them are missable! You can still do everything after the story in free roam.
The Trials in Borderlands 3 are like mini dungeons. You navigate through a special dungeon with lots of normal enemies and then a boss at the end. There are also optional objectives to finish in a certain time limit or to not die, but the optional tasks are not needed for the trophy / achievement.
In the quest log you can see which ones you’ve already completed. They show up as normal side quest markers (yellow exclamation mark) on the map. However, some only show up when going near them. To fully complete them and make the count towards the trophy and achievement you must defeat the boss and put its head in the chest at the end of the trial. Then it will show “side mission complete” and you can fast travel out of the trial area.
You can also play these through matchmaking. Go to Pause Menu > Social > Matchmaking to be paired up with other players online. Due note that the more players are in a session the more health enemies have. It’s entirely doable solo as the enemies will have less health than in co-op. The disadvantage of using matchmaking is that you can’t control what trial you will get. Hence it’s better to know where they are and go there yourself.
After finding the trial quest marker, you must always return to your spaceship (Sanctuary) and put in the coordinates on the command bridge. Then your space ship ports to where the trial takes place and you must exit through the drop pod in the cargo hold. Once you arrive, talk to the NPC with the exclamation point over its head. From there just fight your way through all enemies. There will always be a nice loot chest for you at the end.
The guide below lists all trials by planet and area. The story automatically takes you to all of the areas as part of main missions. If you haven’t been to an area yet don’t bother looking for it, you must advance the story further to get there.
Proving Grounds #1 – Trial of Survival
Starting Location: Pandora, Devil’s Razor
Name in Map Select: Gradient of Dawn
You come to Devil’s Razor during your second story visit to Pandora (fairly late in the game). This happens during main mission “Blood Drive”. Of course just like all the other trials you can return later (even after the story) to start the trial then. Do it any time after reaching this area and once you activated it, track it in your side quest marker. It brings you to area “Gradient of Dawn”.
Proving Grounds #2 – Trial of Cunning
Starting Location: Pandora, The Splinterlands
Name in Map Select: Ghostlight Beacon
The Splinterlands are the area after Devil’s Razor and you also go there during main mission “Blood Drive”.
Proving Grounds #3 – Trial of Discipline
Starting Location: Promethea, Meridian Outskirts
Name in Map Select: Precipice Anchor
You will automatically visit the Meridian Outskirts during main mission “Hostile Takeover”.
Proving Grounds #4 – Trial of Instinct
Starting Location: Eden-6, Floodmoor Basin
Name in Map Select: Wayward Tether
The Floodmoor Basin is reached during main story mission “Hammerlocked”.
Proving Grounds #5 – Trial of Fervor
Starting Location: Eden-6, Jakobs Estate
Name in Map Select: The Skydrowned Pulpit
Jakobs Estate is reached in main story mission “Lair of the Harpy”.
Proving Grounds #6 – Trial of Supremacy
Starting Location: Nekrotafeyo, Desolation’s Edge
Name in Map Select: The Hall Obsidian
Nekrotafeyo is the very last planet you visit, near the end of the story. Desolation’s Edge is found in main mission “The First Vault Hunter”.
That’s all of the Proving Grounds / Trials in Borderlands 3 (BL3). After successfully completing all of them (opened the chest after the boss in each trial), you will earn the “100 Proof” trophy or achievement.