Yampi Desert

Yampi Desert is a desert in the western portion of Osenia. In the general sense, it is a major crossroads of the continent, and travelling through it is initially the only way to reach the town of Alhafra north of it in Golden Sun: The Lost Age.

Several important items and events occur here: you can get the Trainer's Whip, a Jupiter Djinni, the Guardian Ring, and the Scoop Gem as a reward for the boss encounter with the King Scorpion.

Late in the game, when you have the Sand Psynergy you can access a secret cave entrance, and if you have the Teleport Psynergy you can explore a major optional dungeon within that cave called Yampi Desert Cave.

Walkthrough
In the first area, go right, then down. The sandy bit to the right here doesn't lead anywhere, so follow the path around the bottom. Whilst you're here, set Pound to whatever space Whirlwind is set to.

When you reach a poundable pillar, Pound it in. The chest on the other side contains a useful Guardian Ring - equip it on Sheba. Carry on north to the next area. If you spent any real time in Madra you'll notice that the Madran mayor, Town Elder, and various others are trying to navigate the desert, to no avail. You, however, are more equipped to do this. Follow the path to the south to enter a new area.

This area is quite large and there's a Jupiter Djinni to be had. Pound the first pillar you come across. Go north through the path which you've just opened, and continue right, ignoring the pillar to the north and the two sticking out on your path. When you reach the next one above you, Pound it. Go up and back to the left to pick up an Antidote from the chest. Now, there's a visible difference with the wall behind a pillar, so Pound the first one you saw up here. A wall you can climb is behind it, so get up onto the ledge. Go to the left and hop across the pillar. Go down, and hop across the next one. Here, use the two of them to get across, and finally the last one, to reach Blitz. You'll have to fight it.

Use the groove to slide back down, then Pound the pillar next to it. Head right here until you reach another groove. Slide down this one and exit the area to the right. In this area, pick up the Psynergy Stone and pound the middle pillar. Climb up the wall behind it and go north. In the next sandy bit, there'll be a lump moving around continuously under the sand. You'll notice there's a raised Pound pillar on its path - you need to pound it in so that when the lump - which turns out to be a rather large scorpion - gets there, it turns and leaves the area via the exit. This is why you set Pound to L or R. You don't need to time this first one though.

In the next area, you need to, however. Pound the pillar in once the scorpion has been past going upwards. If you do it when it's about to go upwards, it'll get caught in an endless loop, and you'll have to leave the area to reset the pillars. In the third area, you need to Pound the right-hand pillar when it's going to come downwards - if it helps, watch its cycle a few times so you know when you have to Pound. If you do it correctly, the scorpion will get directed into a sandy area surrounded by rocks. If you want, set Djinni on standby ready for summoning, and heal as well. When you're ready to rumble, follow the scorpion onto the sandy area. It'll jump out, and use Scoop on the sand, and it'll collapse. It'll jump in after you, starting the battle.

Once it's over, equip the Scoop Gem on Felix and use Scoop on the sandy circle in the middle of the cave. Now that you're out again, head back to the area where the Madrans are (you'll need to use a groove since you can't Pound things lower than you). When you reach the bit where you slid down a groove in the first place, use Pound on the pillar and climb up the wall behind. If you go pretty much directly left you'll come across a similar sandy circle. Use Scoop here to uncover a ladder. Go through the cave (it's quite short) and when you come out the other side, climb up the walls. The Madrans will notice you up there and will conclude a path must have opened somewhere.

Keep going. Use Scoop on the southeastern sand circle to receive 315 coins--the other sand circles contain nothing. Go into the cave ahead. There are a lot of fast-moving sand currents here - you need to navigate them. For the first bit, get to the very top and run across the sand current flowing downwards. Hop back on at the bottom and get off in between the rocks to reach a chest containing a Hard Nut. Use this on whoever has the lowest Defence. Get back across, and then go upwards (the spaces in between the rocks are big enough to allow you to run across without losing too much ground). When you reach the top, get off on the square surrounded by rocks with a Pound pillar near. Use Pound here, then go past it after stepping on the current again. The chest here contains a Blow Mace, a good weapon for Sheba.

Let the current carry you down again, and get off on the right where you can. If you miss any of these you'll have to go all the way around again. When you get off, go down the ladder and exit the cave. There are sand waterfalls here - you can either let the first sand waterfall carry you off the ledge, or you can climb down the wall to the south. Either way, at the bottom run northeast and climb the wall on the far right. Run across the two sand waterfalls here and use Lash on the rope. Let this waterfall carry you down, but stay on the right-hand side - if you don't, you'll get caught behind the rocks. If you get it right, you can get off the right side of the waterfall and grab a Trainer's Whip from the chest. Let the waterfall carry you off and go back to the right.

Run across these two sand waterfalls again, and climb the wall. Go around the top of the left-hand waterfall, and let the right-hand one carry you on top of the rocks below so you can exit the desert. You can go south here but it leads to a one-way sand waterfall - leading back to Air's Rock. So go northeast, out of the desert. On the world map, head north to enter Alhafra.

Collectibles
Blitz: On one of the elevated portions of a large screen, reachable by Pounding certain brown pillars while leaving certain other pillars standing so you can cross them on top.

Antidote: In a chest in the upper left area of the large area where the Jupiter Djinni can be found. Blow Mace: In a chest in the indoors cave area with the rushing sand streams. 315 Coins: In the screen north of the screen with a small oasis, cast Scoop on the lower-right spot among the sand. Guardian Ring: In a chest in the first screen from the west entrance into the desert, right behind a Poundable pillar. Hard Nut: In a chest in the indoors cave area with the rushing sand streams. Lucky Medal: In an invisible chest in the center of a square-shaped set of nine stones; use the Reveal Psynergy to get it. Scoop Gem: Acquired as a reward for defeating the King Scorpion boss. Trainer's Whip: In a chest in the area with the sandfalls that has the desert's eastern exit. Water of Life: In a chest in the cave entrance to Yampi Desert Cave, reachable with the Sand Psynergy.

Trivia

 * Yampi Desert is perhaps the only location in the Golden Sun series that has three distinctive, separate entrances/exits located on the world map. Its western entrance is reached a short ways southeast of Osenia Cliffs, its north entrance/exit is right below Alhafra, and its south entrance/exit is north of Air's Rock farther east. This last point is generally an exit, though, since it cannot be used as an entrance into Yampi Desert (until much later in the game at least) because of a cliff with a sandfall blocking the way. This sandfall can be climbed up with the Sand Psynergy, but this is hardly useful as a "shortcut" to anything.
 * Incidentally, if you have a cheat device that lets you walk across the area of Angara explored in the original Golden Sun where you can walk into the northeast entrance of Lamakan Desert, you will suddenly enter Yampi Desert as though you entered it from its northeast Alhafra-side - an interesting piece of leftover code on Angara, considering that all the other areas on Angara that would have entered you into locations in the first game were removed completely and keep you on the overworld map.