Lady Gaga is giving away a "Monster Pit key" to one fan on every night of the Born This Way Ball world tour.

The "Judas" hitmaker kicked off her tour in Seoul, South Korea, last night and revealed to fans - whom she calls Little Monsters - the first in line will get to open the Monster Pit - an enclosed area around the stage for hardcore fans.

Tweeting a picture of a skull shaped necklace, she added, "This is a necklace I'll give to the first monster in line every night at the Ball. It's a symbol of the 'key' that opens the pit every night. The real monster pit key will be signed by this fan and returned to me. There'll be 110 necklaces & signatures Mar. 2013 (sic)."

The monster pit is a general admission area of the concert, which will be populated by the most hardcore fans who are first in line to see each show. The tour takes will include 100 shows in more than 25 countries and Gaga admitted her nerves for the opening night: "Nervous for tonight. Hope I make little monsters happy and proud. This is a very special moment for Haus of Gaga. We thank you so much. Enjoy our music, fashion installations & pop performance art tonight."