A map of the Northern Ruins in Chrono Trigger.

Northern Ruins - Enemies
  • Fallen - 1,450 HP - Weak to Fire, absorbs Shadow - Drops Lapis - Charm Elixir
  • Fallen + Soul - 1,650 - Weak to Fire, absorbs Shadow - Drops Lapis - Charm Turbo Ether
  • Flesh Reaper - 1,450 HP - Weak to Fire, absorbs Shadow - Charm Elixir
  • Ghost Knight - 1,280 HP - Weak to Fire - Drops Hi-Ether - Charm Turbo Ether
  • Soul - 88 HP

  • To the north of Choras, the small town in the southeast corner of 1000 AD’s world map, you’ll find the Northern Ruins. Enter, though, and you’ll find your way blocked by a violent, phantasmal figure that you can’t defeat, or even pass. Bring Frog into the fight and he’ll recognize the being... though you still can’t pass.

    Jump to 600 AD. The Northern Ruins are now accessible... to an extent. Much of the ruins are, well, ruined. You won’t get very far. Head into the basement (left staircase) and take out the Ghost Knights guarding the place. These creeps are quite painful to fight, both because of their painful normal attacks and their Grudge and MP Buster strikes upon death. Eliminate them quickly with Fire Techs, as regular blows won't do anything. You’ll need to destroy eight of these things in all to clear this floor of the ruins.

    A villager in Choras complains that his tools are missing. Choras is a settlement in Chrono Trigger.

    This spot is now permanently free of enemies. Leave the chest on the right side of the corridor alone for now and head back out of the ruins. Visit the local Tavern and look for a man drinking inside who complains of missing tools. Jump to 1000 AD and visit the Choras Inn. Another man here is busy drinking. He’ll agree to let you borrow his Carpenter’s Tools. Speak to his wife in the Residence south of here to pick up the tools.

    Return to 600 AD and speak to the man in the Tavern to give him the Carpenter's Tools. Follow him to his Residence and speak to him again to learn that he has a full team of workers. They’ll set about repairing the Northern Ruins. Follow them into the ruins and you’ll discover that they’ve patched a few of the floors, though they can only do so much while there are monsters in residence.

    A team of carpenters finish a day of work attempting to repair the Northern Ruins in 600 AD

    Go up the stairs on your right, now that the hole is gone. At the top and just south of the stairs is a Strength Capsule. Through the next door on your right you’ll face several Flesh Reapers and Fallen. Flesh Reapers can reduce your HP to one in a single hit, so you want to take them down quickly. Fire attacks are your best bet. Make sure you clear out all three squads of these bony blighters before you leave again.

    Return to Choras and speak to the carpenter again. He’ll offer to repair more of the ruins - this time for 2,000 gil. Pay up to send the team of carpenters on their way. They still won’t be done upon arrival back at the ruins, but there are now more accessible areas.

    Frog meets his old friend, Cyrus, one last time in the Northern Ruins of 600 AD

    Head downstairs to the area with the Ghost Knights that you cleared first. You can now get through the door on your right. Put Frog in your party (and Magus, if you want to see him squirm a little) and, after a touching cut scene, you’ll receive an upgraded version of the Masamune. This is the best weapon you can get for Frog, and if you stick the Hero's Badge on him Frog will deal out vicious critical attacks on a regular basis. Look behind and to the left of the grave for a Magic Capsule.

    Return to Choras and pay the carpenter another 2,000 gil to repair the upper floor of the Northern Ruins, now called the Hero’s Grave. This fully repairs the structure, granting you access to the rest of the rooms. Wipe out the foes in the far north of the top floor, namely some Flesh Reapers, Fallen, and physically-resistant creatures called Souls. Fire should do them all in quite nicely.

    There are plenty of chests in the north. Do not open them. That said, you should interact with the three mysterious black boxes on this level... just don’t actually open any of them. If you've been opening these sealed chests up to this point you'll know why.

    Sealed Chests inside the Northern Ruins, a dungeon in Chrono Trigger. If you inspect these chests in 600 AD but don't open them, and then jump forward to 1000 AD, they will contain upgraded items.

    Jump forward to 1000 AD. You can now start opening chests, and since you checked the sealed chests in 600 AD they'll have upgraded items 
    • There’s a Turbo Ether in the basement 
    • There's an Elixir on the second floor
    • One of the sealed chests contains Nova Armor, which upgrades to Moonbeam Armor
    • The second sealed chest contains an Onimaru, which upgrades to a Suzaku, both for Crono
    • The third sealed chest contains a Siren's Kiss, which upgrades to a Valykyrie Bow, both for Marle
    All done? Not quite. You can return to 600 AD and open the same chests and boxes to get a second set of these items (though the black box stuff will not be upgraded, and the weapons won’t be much use to you). Grab everything and you'll be finished with the Hero's Grave.

    There's one last thing to note about this quest. Equip Frog with his upgraded Masamune and put him at the front of the party, then head back to the Denadoro Mountains. Partway up the mounain a Freelancer lobs rocks at the party. Stand still for a moment with Frog in the lead and he'll catch a rock, which turns out to be a Gold Gemstone. Equip this on Frog and he can use the Master Mune Triple Tech with Marle and Robo.