Our Xenoblade Chronicles guide features a comprehensive walkthrough and additional info on the endless amount of optional content in the game.
Walkthrough: Eryth Sea
Your goal is quite a distance away. For now, focus on grinding so you are at least level 36. There are plenty of common enemies that will give you between 200-500 XP, so it shouldnít be too laborious.
East from the starting landmark is a platform that will teleport you to Hovering Reef 1, which features a series of other transports. Check out your map (or the image below) for an idea of where the transport pads will take you. From Hovering Reef 1, the southeastern platform is your first stop.
That will take you to Hovering Reef 2. Again, take the southeast transport to continue towards your goal at the Center Gate landmark.
Youíll be in control of Melia solo for a moment. Take her towards the easy to find goal, and you regain control of Shulk and crew after the cutscene with Melia and the High Entia royalty. Thereís nowhere to go, so chit chat with each of your party members for now.
After a few more cutscenes, you are back in control of the usual gang, and your offer to assist the Entia is accepted. Return to the sea by transporting to the shore, and continuing to Hovering Reef 2. From there, take the southwest platform to Hovering Reef 3, and then the southern platform to Hovering Reef 4. Your contact is straight ahead. After discussing with him, take the transport behind the lighthouse to Reef 5, and then the southeastern transport to your goal.
You are going to face off against four, level 36 Kromar. Itís a difficult battle due to the Defensive Kromarís ability to momentarily disable your arts. Stick with it, and reserve your party gauge for revivals, rather than chain attacks.
When the battle is over, talk to the nearby worker to complete the story quest. Once you regain control of your team, head back to Alcamoth.
Your goal is at the whitewing palace. To get there, take the transport in the southeast corner of the great hall, right at the intersection. When you arrive in the chamber, speak with the attendent. When you're ready to advance the story, agree to rest in the palace.
After Emperor Sorean address the citizens of Alcamoth, Melia will have to face a set of trials within the Entia Tomb. Before making your way to the tomb, the rest of the team will have to defeat a series of Entia scouts, guards, and wizards, in the Whitewing Palace chambers. Focus on a single Entia at a time and make sure to reserve your party gauge in case you need to revive a team mate.
When your team is ready, open your map and skip to the Center Gate landmark on the Eryth Sea map. Head east from the Center Gate(via transport pad). You'll briefly have control over Melia, until she uses the verification device and enters the Tomb proper.
There is an apparent mistake in Special Lever 2 for Regbuilding Colony 6.† It says defeat Earth Nebula at Sap Cave.† I was never able to find a Sap Cave, but I was able to defeat Caris Nebula at the brog lake just before you get to Nopon Arch.†