[Squall Lionheart]

After entering the Tomb, go east whenever you can
Follow the road, you'll end up meeting Sacred the younger brother standing on a pedestal and annoyed by your presence
If you defeat it (or just lower its health considerably) it will run away and the pedestal will rise...
Keep following the way east until you reach a water block, release the chain so the water level is lowered around the tomb...
Again keep going east until you reach the bridge lever and lower it to access the bridge to the tomb, now keep heading straight until you reach a dead end, you'll see the side of the tomb with the bridge leading to it on your right...
Go back and keep following the west way whenever possible and you'll find yourself in front of that bridge and the Tomb of the Unknown King...
You'll have to fight both brothers now, with the difference that they can use special attacks like Mad Cow Special and Minotaur's Mower...

There is a soldier in front of Caraway's Mansion that sells a location displayer if you don't want to get lost, taking wrong ways will get you lost and maybe killed by monsters so it will help to prevent that...