After you give Serena her serene necklace and learn a little bit about Corvus and the Gittish Empire, you should go to the Bowhole, west of Wormwood.
Open the Bowhole
Go east from the entrance to find three blue chests. Then go west. You will find Serena at the top middle of the map, standing in front of the magical barrier that seals the Bowhole. Serena will depart.
The Bowhole - L1
In the first room of the Bowhole, go to the north wall and talk to the ghost to learn the Party Trick Weird Dance.
There are three holes in the ground. You have to jump into one of them. It doesn't matter that much which one you choose, because they all lead to the same area. Just jump into the middle one.
The Bowhole - B1
On the east side of the room, there is a door that is locked from the north side. Approach that door from the north to unlock it and give yourself a shortcut. Go around and open the various chests. In the southeast corner, there are some stairs leading up. Go up them, then unlock the door. It takes you back outside, so you can go back in and jump into a different hole if you wish.
In the northeast corner, there are stairs leading down to the lower level.
The Bowhole - B2
There are chests to the north, the northwest, and the southeast. The exit to the lower level is in the southwest.
The Bowhole - B3
Go straight north to find a blue chest. Then go east and around the room, past the first passage on the left. The second passage on the left contains a red chest that has a Gold Bar inside. Go back north and to the left.
Bowhole LMS Trick
Before going down the stairs, stand in the upper-right corner of the platform with these stairs. This spot on B3 of the Bowhole, standing in the upper-right corner of the platform with the stairs, is a great place for easy EXP because you can farm Liquid Metal Slimes (a.k.a. LMS) here. Just stand in the upper-right corner of the platform with the stairs and wait for a monster to spawn. After a moment, it will walk offscreen to the right. Eventually a Liquid Metal Slime should appear. Quickly run up to it from behind to prevent it from seeing you and running away, then use attacks like Metal Slash and multi-hit attacks like Flailing Nails to increase your chances of killing it before it runs away. Pressure Pointer sometimes works, too. The Liquid Metal Slime gives you a ton of EXP: 40,000 to be exact. This is known by some as the LMS Bowhole trick or the Bowhole LMS.
The Bowhole - B4
Moving on, go down the stairs to B4. Head north to reach a small building. Go inside, then check on the statue.
Gadrongo attacks once per turn. He can use Ground Pound, Heart Breaker, and Burning Breath, as well as normal attacks. Cattle Prod and any other beast-targeting attacks are effective.
After defeating Gadrongo, check the platform to get the Wyrmlight Bow. You will now be able to reach Upover.