Kairo is an island with a tall sand tower next to Savaria. The tower has 3 floors, then the roof. The first floor has 2 Undead Warriors. The second floor has 3 Undead Warriors and an Undead Captain. The third floor has Undead Warriors, Undead Captains, and an Undead General, which you can get the Empyrean Set from. More info about mobs can be found here.
These warriors guard the boss located on the top floor, Ramses II. Each floor has a hole in a certain corner. To reach the boss, you must super jump through the hole to the next floor.
Players must come here to complete the quest Raid Kairo, which requires one to defeat Ramses II.
Defeating Ramses II will change your spawn point to Cumulus Island.
Most players entirely ignore the undead mobs and simply jump through all the floors to the boss. Some use Sky Skates to fly to the top.
A great way to farm EXP is to stand on the second floor and repeatedly use your R move, due to the EXP plus a bonus for killing the undead. Additionally, Radius Stomp is an excellent move for a quick and satisfying farming experience, as it hits multiple times depending on the amount of enemies in its vicinity.
The second floor is also the best area to retreat to when Ramses releases a large tornado that would otherwise send you flying. Staying in the third floor will still cause players to fly, and even glitch into the ceiling.