It's a small outdoor park that hosts concerts throughout the summer. "Boarding House Park" was a park built to memorialize the mill workers who were housed there, and is located in front of the old Boot Mills complex (which in recent years was converted to apartments and condominiums, one of which I lived in until April of this year). On thing you should know about Lowell is that it's the birthplace of the womens labor movement. It was here that women really first began to organize into unions, demand better and safer working conditions, etc. Howard Zinn writes extensively about this area in his "Peoples History of the United States." There is a lot of history surrounding this town, and most of it is very interesting.
The nice thing about this park is that during the day, it's public, and any fencing they put up for the concert is open. What this means is that if you swing by there early in the morning, you can put down your blankets or chairs or what have you before anyone else gets there (did I mention it's all lawn style seating?).
So, any time I go to a concert there (I've seen Richie Havens, the Indigo Girls, Dar Williams, Bob Weir & Ratdog, and loads of others), I can swing by on my way to work, or just whenever I get out of bed that morning, get seats 5 feet from the stage, and just leave my chairs there until the concert starts. Another benefit to this, is if I'm running late getting to the concert (like I was last night), it doesn't really matter, my seats are already saved :).
It's a GREAT place to see a show, and as long as the weather holds out (it didn't one year for the Indigo Girls, and they got rained out halfway through their first set), it's an extremely pleasant night out under the stars listening to good music :).
If you're ever in the area in the summer, I highly recommend checking out their concert schedule at
http://www.lowellsummermusic.org/page.php?page=root/home.htmIf you're curious about the condos and apartments that resulted from the old mill buildings (all of which are still standing and look from the outside as they did 100 years ago), go to:
http://www.boottmills.com/main.htm for the apartments or
http://www.boottcottonmills.com/home.html for the condos.