How do I continue the game in Assassin's Creed 1 after I reach the credits?

How do I continue playing Assassin's Creed 1 in my savegame (Wandering around, trying the air assassination skill, open-roaming, getting all the Templar flags, ...) after I reach the credits in the same savegame?

After going to the credits, I go back to the animus and I'm presented with the memories section. There's no option to continue.

Solution 1:

There is no continue option in the Animus since the story itself is over. You just jump back to a location in the memories section and continue finding flags, etc.

The best place to jump to is Memory Block 6, since from there you will have access to all areas of the map. You could also jump directly into an earlier memory and you will still have all your unlocked abilities and gear, but parts of the map will be locked.