Near the end of the game, you'll enter an expansive dungeon with a barred entrance straight ahead and two sets of staircases, one to each side. To the right is a room with an NPC and a shield. To the left leads to a unique item for the dungeon: a spear that can be thrown through barred entrances.

After retrieving the [Short Spear] and opening the door in the main room, you will have several options as to how you proceed. Eventually, you'll begin encountering NPCs calling themselves "Ancients," who explain you need to find all seven of them to open the final door to the end of the dungeon. A few of these NPCs are annoying to hunt down. You may hunt them down in any order you choose, but for the sake of making this easy to follow I've tried to organize them from "left to right."

(1) In the main room, there is a staircase to the left with an indestructible fast-moving orb in front of it. After retrieving an accessory from heaven that allows you to jump you can find the first ancient by jumping up a ledge set against the north wall across from a vine-ladder to a dead-end room.

(2) In the main room, there is a staircase slightly off right from center beyond 2 breakable skulls. Travel through a teleporter to a room that eventually has a kind of net-like floor near the end. After teleporting once more, keep going straight to find the second ancient.

(3) Continue through the net-like floor area, through another set of teleporters, until you find a sign that tells you to teleport back to the main area by heading north. HOLD ON--climb the staircase to the left to find the third ancient before teleporting back to the main room.

The final four ancients are only accessible after going right through a hallway with floor traps, to a room with a strange goat-like head with a bunch of ball enemies. Throw a spear into the goat-head's mouth to unlock a door under the stairs prior to entering the main area. The music will change after you go down these stairs.

(4) Go down the stairs on the right to a small arrow puzzle. Complete the puzzle to find the fourth ancient.

(5) Go down the stairs on the left into a grassy area with another [Short Spear] at the end. Look to the right to find an arrow statue. Complete a lengthier arrow puzzle to find the fifth ancient.

NOTE: I actually saved this room for last, and was fortunate that I did so as I encountered a bug where one of the arrow statues ended up outside the main play area. I was able to return to heaven and reset the statues through the item bag, but when I returned my character was outside the main play area. I managed to make it back to the puzzle area, but do not know whether I would have been able to exit the room if not for the fact that talking to the final ancient teleported me back to the main room.

(6) Proceed through the door at the end of the hall underneath the stairs to find a puzzle in which you must activate a number of orb/switches separated by platforms that disappear after you step on them. The sixth ancient can be found by activating at least 2 switches (there are some treasures available for activating more).

(7) Climb the stairs above the door to the puzzle room where you found ancient (6) to find the seventh and final ancient.

Once you talk to the final ancient, you will be teleported back to the main room where the final door will now be open.

Thanks to Yama_chan for inspiring me to write this guide and for helping me find ancient (5).