Seward is famous for the Fourth of July Mt. Marathon race that's been run since 1915. The race is a 1.5 mile climb up 3,000 feet on a mud-slick trail. The record time is 43 minutes and 23 seconds set in 1981.
If you are going to be in Alaska during this time and you wish to see or participate in the race, make reservations as soon as possible. It is very difficult to find lodging for that day. If you are in Alaska at the time and are not interested in the race, avoid Seward on July 4th, or you will spend all your time fighting crowds.