Yampi Desert Cave

Yampi Desert Cave is an optional dungeon-style location in Golden Sun: The Lost Age, hidden within the normal Yampi Desert. To arrive at this cave, which contains the boss Valukar and the summon tablet for Daedalus, you should enter Yampi Desert from the Alhafra end, and get to the upper left area of the first screen with help from the Sand Psynergy to get to the cave entrance. You will need the Teleport Psynergy to actually make it into the dungeon itself.

Notable about this cave are the facts it has the Venus Djinni Crystal and that every one of its normal monsters can drop a rare and desirable item.

Walkthrough
Although, technically, you could get inside Yampi Desert Cave the moment you finished Gaia Rock and got the Sand Psynergy, you wouldn't have got much further - the first major obstacle is a teleport circle which obviously you can't get past without the Teleport Lapis found in the game's "normal" final dungeon, Mars Lighthouse.

This isn't necessarily a long dungeon, it just seems to be very confusing. The chest to the right contains a Water of Life. Go up and use the teleport circle to access the main part of the caves. Go straight up. The door in front of you leads nowhere, as does the stairs to the right. Go left, and use Sand to get under the rocks. Use Burst on the pillar to blow it up so you can go through the door behind it.

The stairs straight upwards in the next room also need nowhere for the mean time, so go past them, and around to push the rolling pillar down. Push the other one to the right, then go up. Roll the pillar along and once it stops use Sand to get underneath it (you might want to set Sand as a Psynergy Shortcut, for now). In the next room, straight up leads to some Mythril Silver you can dig up with Scoop. Then, go right, hugging the bottom wall all the way around to the stairs down.

Use Sand to get around the rocks to the other side of the pillar. Use Move to move the pillar down one. You can't get back now, but there is another way around. For the mean time, head down into the next room. The chest to the left in this room contains some Dark Matter. Go down again into another new room. You will encounter a pillar-rolling puzzle in here, involving two horizontal pillars that can be rolled up-and-down and two vertical pillars that can be rolled left-and-right. For the purposes of this walkthrough, we'll label the top horizontal pillar "A", the bottom horizontal pillar "B", the left vertical pillar "C", and the right vertical pillar "D":
 * Push B down
 * Push A up
 * Push B up
 * Push D all the way to the right
 * Use Sand to get under pillar B
 * Push B down
 * Use Sand to get under pillar A
 * Push A down
 * Use Sand in the bottom left corner to get behind C
 * Push C to the right

There you go; you can now proceed to the left. Go up the ladder first. In the next room, hop across the Pound pillar and go down the ladder. Use Move to push the pillar across into its groove opening up a path to the lump moving around in the sand below. You'll find out what this is in a moment; for now, go back into the previous room, and through the bottom exit this time. Go the right and in the chest you will find some Orihalcon (more rare forgeable material!). Up the ladder, use Burst on the pillar. You can now hop across and return to the first main room of the caves.

Go left again, under the rocks using Sand, and enter the next room. The stairs that you ignored before you can now take, since you opened up the path. Assign Scoop as your other Psynergy Shortcut (remember - always keep Move as the other) and wait next to a tile where the mysterious moving lump may appear (it moves in a set pattern). When it appears next to you, quickly use Scoop to dig it out. Crystal, the Venus Djinni will appear, and will attack you. Beat it down with attack Djinni and Psynergies and it'll join your party.

Now, head up and use Pound to smash the pillar into the floor. Go past it and into the room beyond. In here, move the pillar onto the groove to open up one last path. Go back out through the bottom door, past the Pound pillar again, up the ladder and back into the previous room. Go past the rollable pillars to the door at the top of this area, as you did before. Hug the bottom wall in the next room all the way around to the stairs.

Now, the two pillars are in place, so you can use them to access another door on a previously inaccessible ledge. Before you go any further in the next area, save. You are about to fight one of the extra bosses, and he's tougher than you might think. Heal everyone up, but don't standby any Djinn - you will soon see why. Approach the guardian in front of the tablet, and you will be standing toe to toe with Valukar! Following this battle, you can claim the tablet behind him, which contains the Daedalus summon sequence.

Collectibles
Daedalus: This Summon tablet lies at the final room of the dungeon, guarded by the optional boss Valukar. Essentially, the dungeon's "main" goal and reward, following one of the main optional "superboss" battles of the game.

Crystal: This Venus Djinni appears as a brown lump of sand that surfaces at predetermined spots in an area of sand at a regular pattern. To initiate the battle with the Djinni to earn it, bring up your Psynergy menu while the lump appears in the tile right in front of where you are facing, and cast Scoop to scoop up the Djinni out of the ground.

Dark Matter: In a chest immediately visible to the left of the screen when you enter down into a screen from the screen above. Mythril Silver: Visibly half-buried in the ground to the upper left of where you enter one screen in particular. Retrieved with Scoop. Orihalcon: At a chest to the lower right of a screen near an elevated stairwell upstairs. Water of Life: In a chest in the first entrance screen of the cave that is before even the "main dungeon", before the teleport pad.