This is a wonderful route that gives you a complete view of Baltimore's Inner Harbor. It is mostly brick lined so it's a bit easier on the knees that straight concrete. The only drawback can be the crowds, but if you are interested in watching people while you run it's great.
The most critical thing about this trail/path is that it is best to go in the morning or late evening because it can get very crowded--especially in the summer months. Because it runs through the Inner Harbor there are plenty of places to grab a drink or find a restroom
This is mostly a brick-lined trail more than a paved trail with a variety of views of Baltimore's Inner Harbor.
You can start this route anywhere, but to avoid a bunch of overlaps, start on either end. If you start on the other side of the aquarium, you get a bit of everything--concrete, bridges, bricks.
To increase mileage, utilize each of the piers, which you can do--they aren't blocked off. Again, this gives you a unique perspective as you can see both the front of the buildings and the backs (which also happen to be the water views).
You do cross a few pedestrian bridges, but that is the key--no cars. In fact, this whole path has no cars, which is great.
When you get on the other side of the harbor you are traveling right along the water through a more residential section of the Inner Harbor. Again, this gives you a different perspective. Obviously you can turn around at any point, but it is an out and back.
There is nothing better than an early morning outing along the water and this route delivers!