Ozzie's Fort Sidequest - 600 AD Middle Ages
When you speak to the Old Man in The End of Time and he tells you all of the side quests you can do, the second one on his list involves an old acquaintance of ours from earlier in the game, Ozzie. "A fugitive in the Middle Ages, Ozzie, maintains an evil hideout."
Much like traditional Ozzie fashion, you'll be battling Flea, Slash and you'll have to make your way through a tongue-in-cheek trap filled dungeon. I say tongue-in-cheek trap filled dungeon because most of the traps here are very easy to avoid and their real purpose is to entertain the player through silly humor.
There's a few hidden treasures for you to find in Ozzie's Fort as well, in the screen shot below you'll see that in the same room with the guillotine there's a secret room to the south which can be found by entering the hidden passageway.
The hardest part of this entire dungeon is the battle at the end where you face off against Ozzie, Slash and Flea together. During this encounter I recommend you focus on taking them down one at a time, hitting them all with an AoE attack will make them counter your entire team three times in a row. It can get messy really quick this way.
After beating the three of them you'll go up against Ozzie alone and he'll transform into his ice cube just like earlier in the game. Much like before, hit the switch on the wall - you'll fall through a hole in the floor and be in the room just below. Return to the room and a scene will commence with a cat pulling the switch and Ozzie falling down a hole. That's the end of the dungeon, it's not explained what happened to Ozzie, I guess he fell to his death... Poor fella.
Return to the Epoch and travel to 1000 AD, the same location that Ozzie's Fort was at before. There's a town here of monsters and humans that used to be very discriminatory against humans, with Ozzie gone everyone now gets along. Inspect the Forest Ruins in the north which is shown in the screen shot below, it appears as a small blue prism.
Walk up to the blue prism which was previously inaccessible and the Guru of Reason will appear, offering you one of two chests. The one on the left will contain a Safe Helm, an amazing helm which everyone can use and the one on the right will contain Swallow, a sword for Crono.
Safe Helm: Very high armor and a 1/3 reduction of physical attack damage
Swallow: 145 Attack power and +3 Speed sword for Crono (5th best weapon in the game)
It's recommended that you pick the Safe Helm because of the 1/3 reduction of physical attack damage that comes with it. You'll be getting a better weapon for Crono in one or two side quests so picking the sword isn't a good choice.