Cyclocross races are mass start events held in the Fall and Winter and typically 45 minutes to an hour. It’s multi-laps on a closed course on a variety of surfaces (dirt, sand, grass, mud, snow, etc) and conditions (rain, wind, fog, snow). Bike looks like a typically road bike but with knobby tires and good brakes. Super fun racing and a great cardio workout.
I’m an amateur and race my age bracket. Fields range from a few dozen to sometimes as large as 50 guys.
In the Spring/Summer I switch over to Mountain Bike racing and fill in with my favorite wherever I can find them, endurance long distance dirt and gravel road races.
I don’t downhill mtn bike. That’s a sport for the younger and braver!