Walkthrough
Underground Path 5-6 connects Route 5 to Route 6. This path contains no Wild Pokemon or Trainers looking to battle; however, it does contain a number of Items and Hidden Items for you to grab on your way through it.
Obtainable Items
Repel: Northern Path
Lure: Southern Path
Super Repel: Hidden In The Middle Of The Red Path
Nugget: Hidden In The Middle Of The Path By The Fifth Light From The North
Pearl: Hidden In The Blue Path By The Fourth Light From The North
Post Game
Walkthrough
After defeating the Elite Four and starting the Master Trainers Challenge, you will find a couple of Master Trainers within Underground Path 5-6. In total, there will be two of them to defeat.
Trainers
Scientist Murray (Master Trainer): Level 70 Magnemite
Scientist Julian (Master Trainer): Level 75 Magneton