Step 1: Define a "cultural town". A cultural town or city is one whose primary identity and significance are derived from its religious, historical, artistic, or educational importance.
Step 2: Analyze the options.
Canberra is primarily a political/administrative capital.
London and Osaka are global economic and financial centers (though they have rich cultures).
Mecca is the holiest city in Islam, a center of pilgrimage (Hajj), and its entire identity is built around its profound religious and cultural significance.
Step 3: Conclude based on the primary identity. Mecca's foremost identity is cultural and religious, making it the best example of a cultural town among the choices.