Pokémon Pokopia added a lot of new items and collectibles with the first wave of the Expansion Pass, and the Windup Inkay is one of the trickier ones to track down. It sits hidden deep inside the Bubbly Basin area, tucked behind a couple of environmental obstacles that are easy to walk right past if you do not know what to look for. Here is exactly where to go and what to do once you get there.
The Windup Inkay is located inside a large crevice in the middle of Bubbly Basin. Drop down into the ravine and work your way along the right-hand side. You are looking for a pile of sand that partially blocks what appears to be a dead end. That sand pile is actually hiding a secondary tunnel corridor, so push through it.
The crevice entrance in Bubbly BasinOnce inside the tunnel, you will spot breakable rocks on the right wall. This is where 
Ditto's Rock Smash ability comes in. Smash through those rocks to open up a hidden chamber behind them. Inside that chamber, there is a Poké Ball sitting on the floor, and picking it up gives you a constructed Windup Inkay ready to use.
Step-by-step path to the Windup Inkay
- Head into the large crevice at the center of Bubbly Basin
- Follow the right-hand side of the ravine until you see a sand pile blocking a tunnel entrance
- Enter the hidden tunnel corridor behind the sand
- Use Ditto's Rock Smash on the breakable rocks along the right wall
Collect the Windup Inkay from the Poké Ball inside the revealed chamber
What does the Windup Inkay do in Pokémon Pokopia?
The Windup Inkay serves two purposes. First, it functions as a decorative toy that you can place in your environment to raise the comfort level of Pokémon living there. Second, and more importantly for progression, it is a required habitat item for spawning specific Pokémon.
Muddy Playtime habitat setupWhich Pokémon use the Windup Inkay habitat?
The Muddy Playtime habitat requires the Windup Inkay as one of its components. The full list of items needed to 
build this habitat is:
Get all four of those in place and you can attract 
Marshtomp to the habitat. The Muddy Playtime habitat also draws in Inkay itself, which makes sense given the toy. Barboach can also appear in this habitat, though Barboach first needs to be unlocked through story progression before it will show up.
For a full breakdown of every habitat available in the expansion, including spawn requirements and which Pokémon appear where, the Bubbly Basin habitats and Pokémon spawns guide covers everything in detail.
Smash rocks to reveal the chamberIs there anything else hidden in Bubbly Basin worth finding?
The Windup Inkay is not the only secret tucked away in Bubbly Basin. After testing the area thoroughly, the crevice is worth exploring slowly rather than rushing through. The sand pile hiding the tunnel is easy to overlook on a first pass, and the breakable rocks inside are not obvious unless you are actively looking for them.
If you are working through all the collectibles the expansion has to offer, the Starmie Doll location guide is worth checking out next, since that item unlocks Phione and rewards Grubby Pearls and Gold from Dream Islands.
For everything else the Bubbly Basin DLC has to offer, the full Pokémon Pokopia strategy guides collection has you covered.