Edited to up the difficulty from 1.5 to 2.5 since several experienced cachers are having difficulty. Email me if you need a nudge, but please offer some of your thoughts when you do so as to where you think the cache may be.
We've (I've) been wanting to plant some hides along the Merrimack near where V- works in Lowell. I (V-) work in an old mills complex near Bridge Street, for a private company not associated with the actual mills.
Every day (almost) I go walking along the Merrimack River. I have to be honest that I pretty much abhor exercise. Don't get me wrong - I love the outdoors and all of the beauty that this planet has to offer. I just have no motivation or will power. It's part of what I love about geocaching. It gives me incentive to get out - the thrill of the hunt gets me up and moving.
I do really enjoy this walk, though. I start out behind the mills at the beginning of the walkway, and I walk to the red Aiken Street bridge, and then back again. It's a nice little 1.25-ish round trip. I frequently see all sorts of critters during this walk. I have been treated to a Great Blue Heron, baby ducklings, baby geese, and turtles sunning themselves on logs and rocks. The human wildlife can be interesting at times too.
It's an neat area too. There are exhibit stands all over the place that detail the history of the area, and it's some really cool stuff, well worth a read. There are a handful of nice parks. There are some old trains. There is a variety of streetcars that actively run the tracks. Nearby are a Class A-Short Season Minor League farm team for the Boston Red Sox located at a nearby park. There is a popular concert venue here too (building type, not the lawn type), as well as a very well known beer brewing company. Hmmm - wish I could name names, not because I'm promoting them, but so that it would be easier to understand the draw of the area. But, that would be against the Geocaching policy for commercializing caches. There are several museums in the area, and I work right next door to a super busy one. They also hold concerts right on the front lawn of where I work (saw Ziggy Marley the other day!!!). There are also tours of the canal if you were so inclined. All in all, it's a pretty sweet place for things to do and see. You can get a better idea of the things to see and do by visiting the National Park Service website and checking out Lowell, MA. There is also a visitors center on Market Street (there is a cache that I replaced over off Market Street too) you can visit for ideas.
Part of your task will be to figure out parking. It is closely monitored here, especially with it being a university city. It is Free at the visitor center lot (304 Dutton Street) which is about 0.6 from the walking path. Paid parking is available on-street and in city garages.
Please use stealth - this can be a very high muggle area (the walkway as a whole). The walkway is very wheelchair accessible, but I will rate the cache a 1.5 as you probably would not be able to reach it while seated in a wheelchair. Bring your own pen. Enjoy the view! I brought you to a place where the ducks and geese tend to gather, and sometimes you can see some large fish in the water below.