Littleton sits at the junction of I-93 and US Route 302, making it easy to reach by car. It's about 2.5 hours from Boston via I-93 north, 1.5 hours from Burlington, Vermont, and 3.5 hours from Portland, Maine.
There is no passenger rail service to Littleton. The closest Amtrak station is White River Junction, Vermont (about 50 miles west), served by the Vermonter line. From there a rental car is the only practical onward option.
Concord Coach Lines operates daily bus service between Boston's South Station and Littleton, with a stop in Concord, NH. The journey from Boston takes roughly 2.5 to 3 hours depending on traffic. The bus stop is on Main Street, conveniently central.
Manchester-Boston Regional Airport (MHT), about 100 miles south, is the most practical air gateway. Burlington International Airport (BTV) is roughly the same distance to the west, with more carrier options. Boston Logan (BOS) is farther but more connected.