It is constituted by a large bridge with 5 trainers and Pokemon encounters. The trainer are optional, being activated only if you accept the Cianvine Bridge Challenge proposed from Bridgette at the begginng of the bridge.
Cianvine Bridge Challenge
Right when you try to enter the bridge, Bridgette stops you and invites you to this Challenge. If you accept it, you have to beat 5 trainers - not in a row, you can heal pokemon with items and change places before each battle, but you can't go back to city.
Winning all battles and talking again with Briidgette will grant you the Lucky Egg, an hold item that increases the amount of EX granted by battling by 0.25. You can redo the challenge after a day.
Youngster Nigel: Azumarill lvl 64 (Bubblebeam, Play Rough); $512