Well that's fifty-five and a half down...

Well I was partly right, the save point was right before the end of the game, but there was a large chunk left in the the final segment.

After solving the puzzle for the other half of the gateway, which was easy once I noticed there was a chain that I had to climb up, Ico and Yorda make their way to the giant doors. The doors open up and a bridge extends, but when they are half way across electricity from the doorway zaps Yorda and the half of the bridge she's on begins to retract. Ico leaps back to the other side of the bridge, barely making it, but the shadow woman claiming to be Yorda's mother shows up and zaps him off the bridge.

Ico wakes up and finds that he somehow managed to land on some large cages hanging fall below the castle. The rest of the game is a series of simple puzzle areas that Ico has to navigate in order to get back into the castle. Along the way he finds the energy sword that the people that put him there used to open doors, so now he has a powerful weapon and can go anywhere without Yorda. Going back to the room he started in, he finds that Yorda has been turned to stone and he has to fight the shadow spirits of all the children with horns that came before him.

He then makes it to the shadow woman's room and is told that Yorda is to be the new body of the shadow woman. After a big boss battle Ico manages to kill the shadow woman with the sword but has both of his horns broken off and is knocked out cold. All the shadow energy from the sacrificed horned children then goes into Yorda and she gets up looking like the shadow form from the start of the game. She picks up the unconscious Ico and carries him to the bottom of the castle where she puts him on a boat as the castle collapses. After the credits Ico wakes up on a beach and discovers that Yorda had washed up too, alive and looking much more human.

It's a neat game and I could see how speed runs can add to the replay value, there is a trophy for 2 hours, my time was just over 6. Next it's SotC!