As usual, Dzug provides the only sensible answer.
You've omitted to mention which country you're in (or, more importantly, which passport you hold). If you're in the USA, you don't require a visa to enter the UK. See here:
http://www.ukvisas.gov.uk/servlet/Front?pagena me=OpenMarket/Xcelerate/ShowPage&c=Page&cid=10 06977149962
US citizens don't require a visa to enter the Schengen countries which are Austria, Belgium, Denmark, Finland, France, Germany, Iceland, Italy, Greece, Luxembourg, Netherlands, Norway, Portugal, Spain and Sweden. Other countries may require a visa. You should check the website of the relevant embassy. (Even when a visa is required, most countries don't ask about criminal convictions for a tourist visa but a few might).
Chris