One interesting sort of summer adventure involves spending the summer in a university of government research lab. These positions usually are paid (seems to be about $700/week on average), but don’t include travel, room, or board. The list below will get you started, but try searching your local university website for options near you.
Fermilab: the US particle physics and accelerator laboratory (Batavia, IL—Deadline to apply is February 18): 8-week Teacher Research Associates
American Association of Immunology (various labs across the US—Deadline to apply is March 15): 4-6 week Summer Research Program for Teachers
Georgia Tech (Atlanta, GA and other locations across Georgia—Deadline to apply is not yet posted): 4-7 week GIFT program
Harvard University (Boston, MA—Deadline to apply is April 15): 6-8 week Research Experiences for Teachers (RET)
American Physiological Society (labs across the US—Deadline to apply is February 10): Frontiers in Physiology Program