Where have I been?

Solution 1:

It doesn't look like the API supports retrieving how many times a Glitch has visited a street and the time of their last visit, but this information is tracked. If you look at the Encyclopedia of Locations when logged in, each street page will display this information.

So someone wrote a bookmarklet to get around it. It's here; drag it into your bookmarks to use it. Clicking on it will take you to the Locations page in the Encyclopedia, with a few new options. There's a link to 'check' a hub, which will step through each street in the hub and cross it out if you've been there, and besides each location it will add a link to set that location as your in-game destination.

Solution 2:

This has now been implemented in the game. The in game map greys out any street you have not visited, and the updated encyclopedia now shows a checkmark besides every street you visit.

Note that this does not include all locations that counts for traveller and completist achievements, such as Seam Streets and hidden floors. For those you should refer Agent86's answer on this question: What streets have I not visited?