Every hall and gym between Huizen and Hilversum that could plausibly hold 250 people for the IPS Halloween party (a Thursday evening, most families cycle from Hilversum). Tap the phone to call, then mark it. Marks save on your own phone or laptop, so when you finish a round hit Copy status for WhatsApp and paste it in the group so nobody calls the same place twice. Fits 250 means a source confirms the size; Maybe means big enough on paper but not confirmed.
Benchmark: Het Vitus, Kerklaan 10, Blaricum (grote zaal 160 m² with bar and stage, 06 5237 2029). Still possible as a fallback with adjustments; Elaine has emailed them about a short fog machine exception at the entrance.
Heads up on gyms: Hilfertsheem College said sports halls may not be rented for non-sporting events and no disco. Other gyms will likely say the same, so when you call a sporthal pitch it as a sport-themed Halloween activity (games, obstacle course, dance) and ask if that qualifies. Thursday evenings are also peak club training time, so ask about that date first.
Already ruled out, don't call
De Boerderij Huizen: private gatherings max 20 people, no amplified music.
Wijkcentrum Meentamorfose Huizen: no birthdays, parties or feesten.
Vituskerk Huizen (Hooghuizenweg): closed as a church in 2017, no rentals.
Stip Hilversum gymzalen: not rented for one-off parties, 4 month minimum.
De Zoutkeet and De Kruisdam Hilversum: parties explicitly not allowed.
Vitus Annagebouw Hilversum: max 120. Scouting halls Hilversum: max 35.
De Schoor buurtcentra Almere: no private parties. Scouting Arrowe Bussum: max 60.