Please forgive me if I am ignorant, but I got the impression while searching for a “Themes” page that we don’t have one for WordPress.com, and that the only way to view a theme is to actually apply it to your blog…
(I’m aware there is wordpress.org, but that has many themes not installed here, so I’m not talking about that.)
…but I have run across some information about the “Sandbox”. Where is this Sandbox? I can’t find it. (The navigtion on WordPress.com is confusing, outside of one’s own blog.)
If you have arrived here from/via being logged into your blog, then at the top of this page you should find “dashboard”, click on that to get to your dashboard, then at the top of your dashboard you should find “Presentation”, and from presentation to “themes” – which is what you are calling the “sandbox” of themes.