Tales of Vesperia: Definitive Edition

After you have gathered the four spirits and have seen the events in Capua Nor, you can get a scene when you enter Estelle's room in Zaphias. Her room is on the west side of the castle's second floor. After seeing that scene, head to the last area in Zaude. There will be a scene where Rita uses a panel to unlock the Necropolis of Nostalgia.

The dungeon has six sections with eleven floors each. You can only do the first two sections before you clear the game. After obtaining a cleared game file, you can access to the last four sections. Defeat the boss at the very end to earn this achievement.

I want to point out that if you're looking to get every save point, it's important to make sure you slog through every floor of this dungeon, because there is always a save point every 2-3 floors. The problem is that some exit points will skip you past many floors. On sections 1-5, you can take the farthest exit to avoid skipping floors. In other words, if you see two exits, go to the one that takes more moves to get to.

Section 6 (Abysm) is a maze of warps that go all over the place, and I have a solution for you to get to the end and get all the save points.

Section 6: Abysm Guide + All save points
Floor 1: Go left to reach floor 4
Floor 4: Go left to reach floor 2
Floor 2: Go down to reach floor 8
Floor 8: Go right to reach floor 10
Floor 10: Go up to reach floor 9, which has a save point
Floor 9: Go up to reach floor 3, which also has a save point
Floor 3: Go up to reach floor 8
Floor 8: Go right to reach floor 10 again
Floor 10: Go right to reach floor 6, which has a save point
Floor 6: Go down to reach the end

The final boss is quite difficult, by the way. You need to kill the central head, which only becomes vulnerable when all the other body parts have died. The head will then quickly revive its parts, leaving you a disappointingly small window of attack. My strategy was to overlimit Rita and have her spam meteors to do huge AOE damage and kill all parts at the same time. These AOE spells will not hit the central head, though. So once all the boss parts have died (could take a while) I switched to Yuri and spammed destruction field in overlimit. No sense trying to do a big combo because the central head isn't up long enough, you just want to pump out the fastest damage possible. I used every item I could, constantly using specifics, treats, limit bottles, even hourglass when the central head was down. Go all out here. This is the hardest boss in the game. This is what you saved all your items for, right?

Good luck!