What http address does the contributor see when they go to the contribution site?

As with most of the features of SWEET, the URL can be anything that you want. One example is http://walk.yoursiteurl.org. You can also come up with a brand new url that you redirect to from a page on your main site. Regardless of what you choose the URL is your own not ours. Donors and users won't be met by obnoxious and long URLS that cause confusion and are not optimized for search engines.