I voted 10+. I've probably watched a baseball game in 20+ stadiums over the years, but I just realized that most of these "old stadiums" are decomissioned or demolished. Hmmm...just off the top-of-my head:
- Detroit Tiger Stadium
- Chicago Comisky Park
- Cleveland (the 80K seat massive dump) *horrible
- Cincinnati (Riverfront Stadium) *really horrible
- Pittsburgh (Three Rivers Stadium) *really horrible
- Philadephia (Veterans Stadium) *same as Cinci/Pitt
- Milwaukee (County Stadium?)
- Minnesota (Metro Stadium?)
- San Francisco (Candlestick Park)
- Atlanta (Fulton County Stadium)
- New York (Yankee Stadium)
- Montreal (Olympic Park)
- Baltimore (Memorial Stadium) *although I did see CFL football after the team moved to Camden Yards
My favorite stadium of all-time: Tiger Stadium (although I may be somewhat biased)