A lot of people didn't know I was heading to Cuba. This is mainly because Americans aren't supposed to be traveling to Cuba unless they have a proper license issued by the US Treasury's Office of Foreign Assets Control. Constitutionally, we have the right to travel anywhere we'd like but due to our economic embargo on Cuba, it is illegal to spend our money there.
If one wanted to go to Cuba, one might travel to the Mexican border at San Ysidro, cross the border on foot, hop a $15 taxi to Tijuana International Airport and fly to Cuba via Mexico City. There is a $22 tax to travel through Mexico, by the way. You pay this before boarding. You'll also need to pay $15 for a visa into Cuba before you exit Mexico. When you arrive in Cuba, they'll stamp this paper visa instead of your passport. When you leave Cuba, you'll need to pay an airport tax of 25CUC to leave and they stamp your boarding pass.
When you return to Mexico and cross the border back into the US, you present your driver's license as identification (starting in 2008, a passport will be required to cross, I believe 2007 is the grace period) because there is a chance that US Customs will notice your entry and exit stamps from Mexico and wonder where you went.