From Jason Kincaid:

Getting started is incredibly easy — just type in where you’re visiting (say, San Francisco or London), and Google will present a suggested itinerary spanning a three day trip, with around a dozen attractions per day depending on the city. From there you can change the number of days you’ll be staying (Google will show more attractions the longer you stay), and you can also manually adjust the list of places you’d like to visit. You can add a new attraction by entering its name in a text field, and Google will try to find it in its database. All attractions include a star rating, along with its hours operation and location.

I tried it out for Toronto and it’s looking very promising. The locations they pick for a day are more-or-less within walking distance, although you should probably cut the number of attractions in half and spend some more time in truly interesting places.

Also interesting: CN Tower did not appear at all in the itinerary!