To access the Den of Trials, Link must complete nine Levels and/or Drablands Challenges, then return to Hytopia, where The Great Tripini tells the young hero about the newly-discovered Area and the powerful Outfit said to be found within. Though the Den of Trials cannot be unlocked or selected through Download Play, the Links can still access the Den if the "host" Link selects it. However, the other Links will not be able to obtain the Fierce Deity Armor in this mode.
The Den of Trials is divided into portions called Zones, with each portioned Zone being based on the Woodlands, Riverside, Volcano, Ice Cavern, Fortress, The Dunes, The Ruins and the Sky Realm respectively. Each Zone contains five Floors and is accessible from a central hub area with eight Triforce Gateways. The Floors contain Enemies that must all be defeated in order to activate the Triforce Gateway to advance to the next Floor. According to The Great Tripini, all of the Fairies that accompany the Links flee in fear of the Den of Trials, leaving them with only one to start with. However, by reaching the "safe room" on the fifth Floor of a Zone, the Links can obtain another Fairy trapped in a Treasure Chest after collecting the Materials from that Zone and Saving their progress. Each safe room also contains a Squiddy from which supplementary Hearts and Rupees can be retrieved before descending further. When a Zone is completed, its corresponding Triforce Gateway in the hub area becomes activated. If the entire Den of Trials is completed in a single session, beginning from the first Floor, then the final safe room will contain eight Chests with more valuable Materials than the usual three.
A party cannot enter any Zones that has not been reached by the other participant Links, forcing them to begin from the lowest common Zone available. The Den of Trials features several "dark" variants of common Enemies as well as new Enemies that were not present in the other Areas of the Drablands. The final Floor features a triumvirate of Shadow Links, equipped with powered up versions of the weapons available.
For each consecutive safe room that the Links reach, a new congratulatory message will scroll across the screen. These messages will accumulate and reappear at each safe room thereafter, eventually covering most of the screen. The messages for each consecutive safe room are as follows:
"Well THAT was unexpected!"
"You're unstoppable, snickerdoodle! ♥"
"Again? How?! Tell me, tell me!"
"My awe has been inspired!"
"You're legendary, chum! Really!"
If the Links reach all eight safe rooms consecutively, they will also be greeted by a loud round of applause, followed by an audible cheer from Sir Combsly and the onscreen message "Good work, soldier!"
↑"Oh, uh, hi there, little hero dude! Hey, have you heard? They've finished surveying a new, uh, Drablands area. You can, ah, go on a trip there, too. I hear it's called, the, ah... Yeah. The Den of Trials." — The Great Tripini (Tri Force Heroes)
↑"Ol' Trip hears, uh, stuff. Like about a one-of-a-kind outfit at the, um, bottom floor of the Den of Trials... That's mighty...ah...awesome, right?" — The Great Tripini (Tri Force Heroes)
↑" Hey, it's the little hero! Hey. Yeah. Looks like this is the Den of Trials we've been, ah, hearing about... And, uh, it looks like there's some special rules in this place that, um, set it apart from other places. […] They say the Den of Trials has, ah, 40 underground floors. Like...whoa. Yeah. You grab the treasure in each of the zones, and that, um, that completes it. And then you get to go deeper down. From the topmost Forest Zone to the, uh, Baneful Zone at the bottom... Sounds like a long way to, ah, go. Oh, but, ah! If you can complete a zone, then you'll be able to restart from there. So don't, uh, stress, OK?" — The Great Tripini (Tri Force Heroes)
↑"I hear all the, uh, fairies ran away in fear. Yeah. So you only start with, ah, just one! They say there are more, um, hidden away in...uh...oh yeah. In treasure chests in safe rooms." — The Great Tripini (Tri Force Heroes)
↑"Where you can go depends on, ah, the allies you’ve brought with you, it seems. You can only take a trip to the zone just after the deepest one that all fellow heroes have completed. Oh Yeah. It looks like you haven’t completed any yet... That’s OK, dude. Everyone has to start, ah, somewhere. You’ll just have to start at the start. Yeah! That’ll be the, uh, Forest Zone. The Den of Trials is a confusing place. Is there, ah, anything else you wanna know about it?" — The Great Tripini (Tri Force Heroes)