Get your tickets to watch a game at Edward A. LeLacheur Park. If there's nothing on while you're in the area, you might like to check if there's a tour of the facilities.
You'll be spoiled for sightseeing choice in Lowell. Edward A. LeLacheur Park is an ideal place to kick off here, but there are loads of other worthwhile places to consider. University of Massachusetts Lowell, Tsongas Arena, and Lowell Memorial Auditorium are close to the sporting facility and and will cap off your day nicely.