Another trainer lurks on the path to the North, right near the second walking-beam.

Battle: Nursery Aide Hollie (1360 Poke)
Opponent: Cleffa Lv 34, Cinccino Lv 34

Ignore the balance beam for now and head North and West, towards Celestial Tower.  A trainer is lurking in the tall grass here- and well hidden too, being a kindergartener.

Battle: Preschooler Greg (136 Poke)
Opponent: Sunflora Lv 34

In the grass beside Greg is a small clearing with a Leaf Stone in it, a handy evolution item for a number of Grass-type pokemon.  Follow the path North to the end of the grass, then skit away to the East to find another little kid.

Battle: Preschooler Chrissy (136 Poke)
Opponent: Darumaka Lv 34

Past Chrissy is an Elixir and, off to the other side of the path is an Item Ball!  No, wait, it’s a Foongus.

Check behind the right side of Celestial Tower to pick up a TinyMushroom, then enter the tower itself.  Celestial Tower is the ‘graveyard’ area for the Unova region, much as Lavender Tower is in Kanto, or Mount Pyre in Sinnou.  Professor Juniper is waiting here, and she’ll hand you a Lucky Egg, a hold item for a pokemon that boosts its Experience Point gain by roughly 50%.