Remiem Temple
The following steps will tell you how to get to the "hidden temple" known as Remiem Temple.
First off head for the Calm Lands, head north-west and you'll see a trainer mounted on a Chocobo. Talk to her and choose to train a Chocobo, you'll only have to do the first trail (but you'll have to do them all if you want Tidus' Celestial Weapon).
The trail is to ride a wild Chocobo to the finish line, it's not to difficult, just jam the opposite direction to which it is heading and you should keep pretty much straight.
After doing that you can ride a Chocobo around the Calm Lands, mount your Chocobo and head back to the entrance, ride past the entrance into the very corner, look around and you'll see a yellow Chocobo feather. Examine it and your Chocobo will leap over a wall below and reveal the path to Remiem Temple!