MEDICAL LANDMARKS, USA by Martin R. Lipp (McGraw-Hill: $24.95; 550 pp.). Who doesn't like to learn a little something while traveling, but why be conventional about it? Follow the advice of the California physician who has written what is surely the most boggling guidebook of the year. Dr. Martin Lipp lists more than 600 health-related sites, everything from a statue of A. T. Still, founder of osteopathy, in Kirksville, Mo., to the Kam Wah Chung & Co. Museum in John Day, Ore. (above), home of the largest collection of Chinese herbal medicine in the Western hemisphere. Lipp also loves to tell medical tales, and even those who never leave home will be intrigued by the likes of legendary dentist Painless Parker, who once pulled 357 teeth in the light of a single day. "It was a savage and barbaric scene," Parker later noted. "The woods rang with the cries of the wounded." And this is the guy who called himself Painless?