There are free walking tours of the City of York every day of the year except Christmas Day.  However, the number and timing of tours vary throughout the year as follows:

All year round, every day at:
10.15am and 1.15pm

Between 1^st June to 31^st August, every day at
10.15am, 1.15pm and 6.15pm

Additional tours for groups can be pre-arranged in advance – click for more details.