Well, not a real visa, more like an implied tourist visa. The State Dept. says most of the European countries have this rule for US visitors: “Visa not required for tourist stay of up to 90 days.” Would this 90 day limit ever be enforced, as long as you continued to do touristy things?
Bonus question: it actually says (**90-day period begins when entering Schengen countries.) Huh?