Aruba is a small island (75 square miles), located ~20 miles off the northern coast of Venezuala in the Carribean Sea. It is one the Netherland Antilles, and is subject to the rule of the Kingdom of the Netherlands.
The most common mode of trasnportation is by air. A valid US Passport is required. Details on how to obtain a passport can be found here.
For specific State Department information on travel to Aruba, visit this page.
Mountain Project's determination of some of the classic, most popular, highest rated routes for Aruba: