If you are a tourist and you are not willing to spend your money on transportation. That is the perfect option.
There are several lines that will take you to the most popular tourist spots.
The best part is that you could hop up on the trolley for free. The disadvantage for me was that I was using it in July, so it got pretty stinky inside at times.
If you are only spending a few days in Chicago, the Chicago trolley is not a bad idea. It takes you around downtown Chicago and stops at major attractions sites. Also the guide gives you an insight on the architecture and history of most of the historic buildings and of the city. Tickets are about $20 per person for the whole day. You can get off at any trolley stops and catch another one any time you like. Trolleys come by about very 30 minutes.For routes, check the website.
There is a free trolley that runs to and fro Navy Pier to the museum campus (Shedd aquarium, Field museum and Adler planetarium), Art Institute, State and Michigan avenue shopping district and Lincoln park. Look for the sign "free trolley".
You can pick up a trolley every few minutes at any stop during operating hours, so you shouldn't have to wait long at any stop. Here's one of the signs that show you which route to take (each bus has a symbol, such as a star or a square, in the window identifying the route it drives).
There is a free trolley that operates in Chicago from Memorial Day through Labor day, and during the winter holiday season, (except on the holidays themselves). You can take the trolley from just outside Marshall Fields on State Street (there's a sign for the waiting area) to Navy Pier or to Michigan Avenue. You can also pick it up at either train station (Union Station or Oglevie), so it's great for saving you a long walk to the typical tourist attractions. Maps are available inside the trolleys for their routes, and signs by the trolley stops show where each of the three routes stops.
Beware of the lines, though--you can wait quite a few minutes for a trolley that isn't full on busy shopping days.
There are several free trolley's that travel up and down Michigan Avenue, and to Navy Pier, Grant Park and several other area's. The trolley's are very convenient, great for tourist because they go to the tourist hot spots, and they are FREE.
This is the free trolley that you can catch at places like Michigan Ave. to take you to different landmarks around the city for free.
These "trolley" tours are run by Chicago Trolley & Doubledecker Company -- this stand was just outside Orchestra Hall on S. Michigan Ave. near the Art Institute.