I made a reply up above, but the best example I have is Ferry Bar Park (pic I took here: https://www.flickr.com/photos/40423570@N07/24766355732/). Another is Fort Armistead Park, which is probably my favorite park to take sunrise photos in (examples: https://www.flickr.com/photos/40423570@N07/25705211566/, https://www.flickr.com/photos/40423570@N07/30999597372/), but the place is an appalling dump, you can find some reviews of it here: https://www.yelp.com/biz/fort-armistead-park-baltimore

Round Falls, while not an official park, is an open area along the Jones Falls trail that runs through Baltimore that is in complete disarray (see http://thebaltimorechop.com/2012/06/26/round-falls/). Riverside Park was also pretty dirty when I visited, though it has good reviews online, so maybe I went on an off day.