The project has many dimensions, but one of the most interesting is the maps tab, which allows you to see interactive maps from different eras in London's history.
Interested in old manuscripts? Find a first edition at Hodges that has marginalia but don't know how to read old handwriting? You can learn about paleography (the study of handwritten texts) and even take a course in reading old handwriting. The National Archives also has a nice online course on paleography.
This is a very basic, unfussy, but really useful online DB of scanned images from the LWL, which is part of Yale University's library system. They specialize in images, including prints, paintings, playbills--all kinds of "ephemera," or one-off single sheet things that won't show up in EEBO or ECCO.