Friday through Sunday, May 23–25, Ardenwood Historic Farm in Fremont hosts its annual Rail Fair, running 10am–4pm each day. Admission is $10–$14 for adults, $6–$8 for children 4–17, free under 3; check the East Bay Regional Park District site for the exact current tiers. The farm sits at 34600 Ardenwood Boulevard, Fremont — no BART direct, so drive or coordinate a ride; the Newark BART station is roughly four miles out.

What makes this more than a train-themed weekend at a petting zoo: Ardenwood runs a narrow-gauge steam railroad as part of its regular operation, and the Rail Fair layers on visiting equipment, model railroad layouts, and hands-on demonstrations that the standard farm visit doesn't include. The Memorial Day weekend timing means all three days are realistically accessible, not just the holiday Monday.

Practical notes: parking is on-site and included. Bring cash for food vendors — the farm's concessions are not card-reliable. Crowds peak Saturday midday; Sunday morning is the quieter window if you're coming with kids who need breathing room around the equipment.

If you've got two hours: arrive Sunday at 10am, do one loop on the steam train while it's not yet packed, then walk the model layouts before the gates fill. Skip the gift shop until you're leaving.