Also, George Washington University and Carleton College host summer programs for undergraduate women in mathematics. The Alice T. Schafer Prize goes to an outstanding woman undergraduate each year. The National Security Agency offers a popular internship for those interested in cryptography, signals, and number theory. Take classes from famous Hungarian mathematicians. Focus is on problem solving.
Classes are in English.
The Putnam exam each December is a nation-wide collegiate competition in mathematics. Each school gives out the exam simultaneously. Each summer the Institute for Advanced Study holds a joint workshop called the Park City Mathematics Institute in Park City, Utah, where there are separate programs for undergraduates, graduate students, researchers, and high school teachers. Generally a lot of opportunities for undergraduates to learn math and meet lots of people.