Lowell is not a place most people seek out as a tourist destination but it holds some unique places to visit. I stumbled upon Lowell on a business trip and I can make some recomendations...
Park at the Visitor Center for the first urban National Park. Be sure to sign up for the boat tour of the canals and visit the Boott Cotton Mills to learn about the American Industrial Age and the "Mill Girls". It's also an introduction to the labor movement in America.
If you have additional time visit the Whistler House Museum of Art, which is in walking distance from the National Park. It's an amazing testimony to Lowell's famous artist, James Whistler, and has a lovely collection of 19th century art.
Speaking of art, be sure to see the art galleries and studios at "The Brush", which is adjacent to the Visitors Center at Market Street.
Take a walk to St. Anne's Church and hope you get lucky, like I did, to meet the sextent, Paul. He took me on a tour of this amazing house of worship which includes several Tiffany windows. I even got to go up in the bell tower that hosts several multi-thousand pound bells that are still being rung!
If you want a place of quiet contemplation and beauty, consider visiting the Victorian Lowell Cemetary. It's a great place to walk.
Lowell has had a rather rough and tumble reputation as a city of immigrants. It still is, but it celebrates it with lots of festivals that sound very interesting. I hope I have the opportunity to come back and explore more.