You should go searching for nearby wireless networks using a Wi-Fi capable device such as laptop, iPad, PDA or a handheld gaming console. Trolling around for wireless internet is called ‘Wardriving’. An extensive software catalogue for wardriving on various platforms is available online. Notable examples include NetStumbler for Windows (stumbler.net), Kismet for Linux (kismetwireless.net) and KisMAC for the Mac OSX (trac.kismac-ng.org).
However, it is quite cumbersome to sniff out Wi-Fi hotspots with an open laptop in one hand and plenty of portable Wi-Fi-capable devices such as the Apple iPhone and certain mobile phones that can do the job equally well. Applications like Stumbler for the iPhone and Barbelo (darkircop.org/barbelo) for S60 3rd Edition devices such as the Nokia 95, N82, etc. can use a phone to detect 802.11 networks.
Often, it is possible to connect to public and open wireless networks that belong to restaurants, cafes and the like, but it is also likely that you will discover open Wi-Fi networks which belong to private organizations and individuals and which are not meant be accessed by all and sundry.
It is inadvisable and unethical to piggyback on a private network and definitely illegal to delve beyond just internet access while connected to any network – even if the computers and files on the network are visible and accessible.