Free walking tours are a phenomenon that has popped up pretty much everywhere where tourism has grown. They are a super cool idea especially for people like us who have no interest in shelling out $50+ for a bus sightseeing tour.
Free walking tours normally are run by local students or youngish people who work for tips.
The companies that put them on often also offer paid tours, private guiding, cooking classes etc. so the free walking tours serve as promotion for the business - lots of incentive to do a good job.
Lili and I did a free walking tour in Prague, and all three of us took one in Barcelona.
Our Barcelona guide was Juan Carlos Colon, who is half American half Catalan. (Please note we do not say Spanish because the Catalan are very particular about their own identity.)
We had a great time on our walk, and spent a fascinating three hours touring the old town. We saw Columbus's contract with King Ferdinand, Joan Miro's birth home and the school where Pablo Picasso studied art. And we saw many wonderful stores and galleries.
After the walk we had our one and only restaurant meal in Barcelona - at Maoz falafel joint. We had eaten at Maoz already in Paris, so we knew to expect the super quality and backpacker prices. And Lili got some fries and Fanta -rare treats both.