Fortnite's seismographs are your key to completing the latest challenge in Fortnitemares.
A new challenge in Fortnite/Fortnitemares has players deploying seismographs in Misty Meadows or Catty Corner as part of the new Ghostbusters: Afterlife crossover event. Much like the titular busters, we're using tools to hunt down ghosts, or maybe cube monsters. I don't know. Fortnite lore is a bit of a Hellraiser puzzle box these days.
This is the first actual challenge of the Ghostbusters punchcard, so if you want to earn a bunch of extra XP and free cosmetic items, you'll start here.
Your first step is to speak to the Containment Specialist, a fellow dressed up exactly like a Ghostbuster hanging out in Cape Cod south of Catty Corner. You'll find him specifically in the barn containing what is clearly the Ectomobile hidden under a tarp.
Speak to Containment Specialist and select the "!" option. He'll give you your first quest to deploy seismographs in Misty Meadows or Catty Corner.
You only need to deploy three seismographs, so my suggestion is to just head north/slightly northeast to Catty Corner. I'll be honest, I had a lot of trouble finding seismographs in Misty Meadows, and it's much bigger than Catty Corner, so don't even bother.
Once you're at Catty Corner, here's where you'll find seismographs, marked with red squares. You'll recognize them as the usual blue transparent outline.
Seismograph location 1: Behind the garage/gas station.
Seismograph location 2: At the start of the driveway on the north side of the gas station/garage.
Seismograph location 3: Across the street in the actual Catty Corner area, on the northwest side out in the open.
Once you've interacted with all three, you've completed the challenge. Nice work, buster. For your trouble, you'll get 30,000 XP.