The walk starts at Great Portland Sreet tube from where it is a short distance to formal, laid out Avenue Gardens part of Regents Park. After this you can either continue up through the northern end of the park or make a (probably not quick) detour left to the Queen Mary Rose Gardens.
Panorama of Regents Park - Rose Gardens in Queen Mary's Gardens supplied by Panoramic Earth
At the top of the par we pass by London Zoo and then cross the Regents Canal and along Prince Albert Road to Primrose Hill. For those inclined, it is a short, but steep, walk to the top for stunning panoramic views over the city. Exit at the north-east corner onto Regents Park Road and continue north along a pretty row of boutique shops and cafes - a good place to grab a slice of cake and drink.
Continue across the railway bridge and then head right down to Chalk Farm tube where there is a fantastically painted building. At this point you begin the return trip turning south and heading back to Camden Market. This is where you can loose a lot of time browsing the various stalls selling almost anything you could imagine, including a lot of local arts and crafts.
The weary can opt to end their walk here or finish it by either wandering up Parkway past the Jazz Cafe and a fantastic health food shop or along Regents Canal. Both routes end up near the north end of Regents Park and from there you head south to end up back at Great Portland Street.