Sail your Waverider and clear out every monster encampments you can find. When you finally found hilichurl encampments, you can attack them with Waverider armament or just defeat them directly with your character.

I found some guide from Paimon in hoyolab forum, here’s the details:

Waverider Armaments

Main Cannon, Make Ready... Fire 2 Kind Of Monsters Tower — 2 Kind Of Monsters Tower

The Waverider is equipped with two types of armaments — the Swiftstrike Cannon that shoots Swiftstrike Cannon and Heavy Cannon. The Waverider’s two armaments are capable of dealing considerable damage to light floating towers, but cannot damage heavy floating towers.

You can use the Waverider to destroy light floating towers and defeat enemies by sending them plummeting into the sea.

Destroy Enemy Wind Barrier

You can also climbing to platform directly and defeat the enemy. As for tips, use charged attack to throw enemies to water. If the enemy is in another platform, use archer charged attack to knock them back and throw the enemy to water.

Main Cannon, Make Ready... Fire Enemy Camp Protected By WInd Barrier — Enemy Camp Protected by Wind Barrier

Some enemy encampments may be shielded by a Violent Wind Barrier. Travelers will need to use the Heavy Cannon or Explosive Barrels to destroy it.

Main Cannon, Make Ready... Pity Pearl — Pity Pearl

Collect pity pearls to greatly decrease the cooldown of your Heavy Cannon and bring the barriers down faster.

Beware of Whirpool!

Main Cannon, Make Ready... Fire Whirpool Is Dangerous — Whirpool is Dangerous

There may be Whirlpools near the sea monster encampments. Please avoid the Whirlpools during the challenge.

If caught by the Whirlpool, the Waverider will start taking continuous damage and Travelers’ Stamina will be rapidly consumed. If the Waverider is destroyed, Travelers will automatically be ejected from the Waverider.

After defeating all enemy and reinforcements, you will obtain currency called Shiny Floatsam. By collecting this currency up to certain numbers, you can get following rewards from challenge quest and buy items from event shop.

Challenge Rewards

Requirement	Rewards
Collect 200 Shiny Flotsam	30 Primogems	20,000 Mora	1x Waverider Repair Toolbox
Collect 1,000 Shiny Flotsam	30 Primogems	20,000 Mora	–
Collect 2,000 Shiny Flotsam	30 Primogems	20,000 Mora	–
Defeat 30 enemies while boarding a Floating Tower	2x Hero’s Wit	20,000 Mora	–
Defeat 60 enemies while boarding a Floating Tower	2x Hero’s Wit	20,000 Mora	–
Use the Waverider’s Heavy Cannon or explosive barrels to destroy 5 Violent Wind Barriers	2x Hero’s Wit	20,000 Mora	–

Shiny Floatsam Event Shop

Item Name	Price	Stock
Crown of Insight	500	1
Northlander Billet Trove	500	1
Blueprint: “A Guide in the Summer Woods“	100	1
Blueprint: “A Messenger in the Summer Woods“	100	1
Blueprint: “Pure Gorgeous Summer“	200	1
Philosophies of Freedom	50	2
Philosophies of Resistance	50	2
Philosophies of Ballad	50	2
Philosophies of Prosperity	50	2
Philosophies of Diligence	50	2
Philosophies of Gold	50	2