I LOVE spinning classes- they keep me going hard, i leave tired and sweaty, and its a great solution for me since I am at school and my bike is at home (I live in a city and theres really nowhere for me to ride).
Luckily, they are free at my YMCA with my membership, because I will do 4+ classes a week. Two nights a week the class, which is 45 min long, switches to an hour and they have a professional cyclist come in and teach it- they call it "Road Race Training" and we watch the Tour (its kinda like being in a big theatre- the entire back wall is a movie screen).

However, given the choices, I'd rather be a home in New Hampshire, biking long loops w/my mom outside!