Follow the path, defeating the enemies that spawn along the way, to find a new weapon surrounded by thorns. These are the Fire Bellows, capable of spewing flames wherever the Kid aims them. Use them to defeat the enemies that attack and destroy the thorns in your path. A bar in the bottom-right corner of the screen shows how long they can generate fire before needing a recharge, which can be done by simply pausing your attack. There are two paths that can be taken here, one north and one south. Burn through the northern path first to find Something Heavy, then burn through the southern path to proceed.
Past a field of Stinkeyes will be an area where Wallflowers and Pincushions spawn. Defeat them all and a new memento, the Pecker Nest, will drop into the area. Speaking to Zia about this memento at the Bastion will summon a Pecker to the hub. This is the final pet that can be found throughout the game, so make sure to have all four for an achievement/trophy. They also contribute to a Vigil at the Memorial that requires the Kid to collect the lost mementos scattered across all locations.
After retrieving the Pecker Nest, you should see two paths, one east and one west. Burn through the thorns on the eastern path first to find Something Pointy and the Arsenal. Along the western path are many enemies and many thorns, so prepare accordingly (take note that the Fire Bellows aren't the only weapon capable of destroying the thorns, if you'd prefer to use another). At the end of the path will be the Shard.
Backtrack after picking up the Shard to find another path. This path leads to a Skybridge that sends the Kid to another area where many more enemies attack. Take the northern path past the enemies and thorns to find the Skyway that takes the Kid back to the Bastion.