The Spanish Branch's Sandbox page includes a direct link to one's sandbox in the sidebar, by using the following code:
[[div class="menu-item"]]
[[module ListUsers users="."]]
[/%%name%% My Sandbox]
[[/module]]
[[/div]]
The code should be pretty self-explanatory for mods and admins. It basically generates a link using the syntax sandbox-url.com/username, wich should always link to a valid page because a user's sandbox is supposed to be their username.
I think the SCP Sandbox III should implement the same system to ease access to our sandboxes, because a lot of people hate to type in the URL manually or simply don't like to bookmark their sandbox.