Fenway Park is the oldest Major League baseball park in the United States. Its small, intimate atmosphere really allows you to feel like you are "in the game." On a warm summer night there is nothing better than going to the park, sipping a beer and watching the game. The park is situated right in downtown Boston - so it is very accessible if you are visiting the area. Tickets to the game can be difficult to get, so check with your hotel concierge about getting tickets before heading over to the park.
Tip: Tickets sometimes open up 24-36 hours before game time, so you may want to try the Red Sox website once you are in town, or contact the box office directly. In addition, the Red Sox permit lines to form for game day tickets - a limited number which are available - five hours prior to game time (though, some fans do camp out overnight for tickets to the most popular games, which is permitted).
