At the base the hill where Sahasra Slope Skyview Tower sits, you find Sahasra Slope Cave.

Cave Location

Sahasra Slope Cave is located at 1366, -1191, 0132, at the base of the hill with Sahasra Slope Skyview Tower on it.

Explore the Cave

At the west entrance to the cave, you find boulders in the wall that you can break down with a heavy weapon or by throwing a bomb flower at it. Beyond this, there is another wall of boulders that you have to break down. Beware of the three Horriblins just beyond these walls.

After you defeat the Horriblins, open the treasure chest at the top of the slope and collect the other items around it. You can also find Traveler's Claymores, and there are rocks in the cave that you can Fuse to them, if you run out of bombs and/or heavy weapons that can break the boulders.

Then go southwest to find another wall blocked by boulders. If you can break down all the boulders, you find several tunnels. One tunnel goes southwest, and in that tunnel there is a boulder against the wall with two small rocks next to it. If you move the boulder, you reveal a hole where you will find a Bubbulfrog and some ore deposits.

Exit the Bubbulfrog cave, and then you can go to the center of this small room where you moved the boulder away from the wall, and use Ascend to enter the room inside of the Skyview Tower above. From there, you can open the door as explained in Sahasra Slope Skyview Tower.