The highlight to any trip to Tehran—if you can manage it—is a visit to the scene of the most spectacular hostage-taking in recent history, the US embassy, which Iranian students stormed in November 1979, holding 52 Americans hostage for 444 days, and dumping US diplomatic correspondence on the street in a spectacular premodern WikiLeak.
For Canadians and Brits (let alone Americans), getting there is not easy. Neither country has diplomatic relations with Iran at present. Canadians must mail their passports to the Pakistani Embassy in Washington, DC, Brits must apply to the Omani Embassy in London. (Britain and Iran have only recently agreed to open consular services following a meeting between Iranian President Hassan Rouhani and British Prime Minister David Cameron at the UN in New York in September 2014).