This. You must complete all of the community center rooms (or joja town development upgrades if you chose that route.). Watch the cutscene before noon or one I think on a sunny day. Then shortly after he will send you the letter that it is unlocked. You must read the letter first I think as well with most things Willy related. You will need 200 pieces hardwood, 5 iridium bars and 5 batteries to complete the boat so gather those too in the meantime.
Yes. Apparently letter reading is a thing in this game. And following your quests, knowing whether they're even active yet.
Getting to Level 100 in Skull Cavern and finding a Chest containing 15 Parsnip Seeds is... Anticlimactic.
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Farmer Bobbi sits there on the Chest cleaning off her Serpent-nibbled knees, hoping her scabs will at least smooth over yet be worthy of some Pelican Town curiosity. Well, assuming they won't just make her look like a 12-year old out playing at the park too long. She slowly opens one pack of Parsnip Seeds placing each small, flat, brown, stripy one singly between her teeth to crush it. Enjoying the earthy taste and pondering... what she might have missed? Something compelled her to get here but for the life of her, she couldn't fathom from where the urge had sprung.
Crunch... another seed.
Why couldn't these be Beet Seeds? Not that they taste better, Bobbi had no idea. But she needed to grow Beets and put them in the Mayor's fridge for some utterly inane reason because some fool was leading her around on a wild goose chase. That her curiosity just wouldn't let go because it was almost fun though she'd never admit it. She sooo wanted to just walk away but she was as hooked as the Fish she occasionally caught when not dozing by the lazy river.
Downing a Cheez, Bobbi hopped off the Chest and tossed the remaining Seeds into her pack thinking that Pam might like a Parsnip and her birthday was next month. She looked around the small cave floor one last time, now becoming decidedly annoyed.
And then angry.
A scowl on her face, she pulled out her stack of Bombs and stomped towards the ladder beckoning her deeper into the Cavern. "I've had enough of this!" she yelled to everybody in particular.
Foot on the top rung already starting her descent, "It's time for mayhem!" echoed throughout the Caverns.