If you're looking for a costume idea, here are some of the best! ... If you want to make your own, the original website has design specifications

Prince Caspian costume worn by Ben Barnes on display...

The titular 'Prince Caspian' is played by Ben Barnes in the second Chronicles of Narnia movie, and this is the costume he wears in the opening scenes in his dramatic escape from his evil uncle, Lord Miraz's, castle into the surrounding woodland.

Original Prince Caspian costume worn by Ben Barnes
Original Narnia Prince Caspian costumeBen Barnes Prince Caspian movie costumeBen Barnes Narnia Prince Caspian costume
This original costume, designed by Isis Mussenden, was photographed on display within the Journey into Narnia: Prince Caspian walk-through attraction at Disney's Hollywood Studios in Orlando on September 22, 2010.

The Chronicles of Narnia: Prince Caspian movie poster
Prince Caspian movie poster

Actual Lord Miraz and Prince Caspian costumes on display
Miraz and Prince Caspian movie costumes
Be sure to also check out Prince Caspian's battle armour and King Miraz battle armour here at Hollywood Movie Costumes and Props.

Dress like Prince Caspian and buy the Halloween costume: Narnia Prince Caspian Costume - Disney Child Costume deluxe