Fern Britton, presenter

Southampton

I have loved this area ever since I was working there for TVS back in the late 1980s presenting Coast to Coast with Fred Dinenage. This is the route I would most love to go on: heading east from Southampton, the cycle lanes on the Itchen bridge take you high above the river Itchen as it joins Southampton Water. This is one of the most popular sailing areas in the country, and you will often see yachts with their brightly coloured sails speeding across the water.

Beyond Woolston you soon join a path for walkers and cyclists, running alongside the water. The path runs parallel to a beach and there are views over Southampton Water towards the New Forest, and there are also views back towards the docks and the National Oceanography Centre. Royal Victoria Country Park with its handsome red-brick heritage centre is the next highlight, soon followed by the winding narrow streets, tea shops and pubs of the pretty marina at Hamble-le-Rice.

Olivia Williams, actor

Cambridge

Cambridge is the perfect cyclist's day out: back routes, cycle paths, bridges, rivers, views ... it's a historical/architectural/artistic tour, and all in mercifully flat terrain. When I was there as a student, every journey started at Newnham College. From Basil Champneys' lacey Edwardian architecture you can give yourself a Modernist jolt on the Sidgwick site, and then head for the Sterling Library and the University Library (every book ever published and the best flapjacks in the county).

Don't miss the Wren Library in Trinity College and the Bridge of Sighs at St John's, but if you need to escape the whole varsity thing, there is a haven of peace - Kettle's Yard is a house-turned "art space" with the kind of minimalist exhibits that go well with your Farrow & Ball wallpaper.

Cover some ground and head out to the Queen's Head at Newton for a pint of Adnams served at the right temperature with a slab of stilton and a hunk of brown bread. Back in town in time for evensong at King's College, followed by a leisurely scoot over Clare bridge. Along the backs to the Granta pub, for a nightcap overlooking the millpond.

Now that I have two children, I have two child seats, designed by the masters of the cycling universe (the Dutch), which allow me freedom from the misery of toddler-bored-in-traffic-induced hypertension.

I have just got a job in LA (in Joss "Buffy" Whedon's new TV project called Dollhouse) and have rented a house in Santa Monica, the only place in LA to have bike routes and buses with bike racks.

James Cracknell, Olympic rower

Central London

I love cycling and it keeps me fit - but for short journeys it's also often the easiest way to get from A to B and it also keeps my carbon footprint down to a minimum. This is a brilliant route along the river and you don't double back on yourself, as you're on a different side of the river on the return. I've run it, pushed a pram down it and now my wife Bev [presenter Beverley Turner] and I love taking our four-year-old son, Croyde, on bike rides along it. You're in the centre of London and there are no cars, which is a rarity. Most of the ride is along towpaths so you can relax a bit.

We start at Kew bridge, drop down on to the north side of the Thames and continue along Strand on the Green. When we get to Chiswick bridge, we go down the steps past Tideway Scullers rowing club and then follow the towpath. It brings you through the deserted Chiswick streets and then Furnival Gardens - there are some great riverside pubs to stop off at on the way too. When we reach Hammersmith bridge, we cross over to the south side of the river. Following the towpath back, past Barnes bridge and the brewery at Mortlake, we then head under Chiswick bridge and along the river back to Kew. It depends how often we stop, but we tend to do this route in about an hour; it's about nine miles but you can always cross the river earlier on if you want to cut your ride short.

In terms of improving your fitness, cycling is really up there. To calculate how many miles I've travelled over the course of a month, I use the Sports Tracker facility on my Nokia phone - I always have my phone on me anyway, so it's easy to use.

Wayne Hemingway, designer

Portsmouth

The Puffing Billy route from Havant (6.5 miles on the national cycle network's route 2) makes for a great family outing, with fantastic birdlife coastal views and great places to stop picnic, skim stones and fish. From Havant town hall you follow the Hayling Billy railway path southwards until the busy Langstone bridge. If you decide to extend the ride, at the end of the track, there's something for everyone. It's a short ride following the Hayling Island beaches, with possible stops at the fun fair, the surf club, the public golf course with the cool 1930s clubhouse, and on to the little foot-and-cycle ferry to Portsmouth.

From the ferry the ongoing ride takes you along the esplanade to the Sea Life Centre and on to Portsmouth and Southsea railway station where you can catch the train back, or - better still - do a bit of shopping and eating at Gunwharf Quays then take a trip up the Spinnaker Tower. A decent bit of pasta is enough to persuade the kids to then cycle back to Havant via the secondhand shops of Southsea high street and then along the western side of Langstone harbour.

Wayne Hemingway is a patron of Sustrans (sustrans.org.uk)

Fearne Cotton, presenter

West London

As a Londoner, I am really proud of my city.

I live in one of the prettiest parts, and find that getting on my bike helps me make the most of the city's green spaces. Just being near the Thames makes me feel connected to London's history and so the cycle route I would recommend starts from the Richmond riverside and follows the Thames Path past Kew Gardens and all the pubs on the river. It would take you through Barnes village and over Barnes common on to Wimbledon common, Richmond park and back towards the river. The route is mostly traffic-free and takes you past pubs and cafes if you need to stop off.

Jon Snow, news presenter

Ardtornish, Argyle

Travel along from Lochaline to the Drimnin road and cycle for 13 miles to Drimnin. Then take a taxi boat to Tobermory, have a tea break, and then cycle back along the sea to the Fishnish ferry and back to the mainland at Lochaline. The route is mostly on B-roads and very quiet main roads. Highlights are the lighthouse on Eilean Musdile, which can be seen on the way into Tobermory harbour, the harbour itself (the setting for kids' programme Balamory) and Aros castle. All of this has the stunning scenery with Ben More in the background. The Mull area is an excellent wildlife-spotting location, with dolphins, puffins and the like.

Jean-Christophe Novelli, chef

East London

This route, which is about 22km in length and should take about two hours, provides a wonderful exploration of the City and East End. Much of it uses the national cycle network. It includes the pubs and clubs of Hoxton, food and flower markets, the "green bridge" at Mile End, London's canals, the Isle of Dogs, and the backstreets and historic sites in Deptford and Greenwich. It needs to be done in a clockwise route, though, because of the one-way streets. It's best done on a Sunday when Columbia Road flower market, Borough food market, Broadway and Greenwich street market are all open.

Start in Greenwich at the foot tunnel next to the National Maritime Museum, then head past the Cutty Sark site and Greenwich market, through the historic backstreets of Deptford close to the modern Laban arts centre on Deptford Creek. Follow the cycle path close to the Thames, past Brunel Museum in Bermondsey, and around the back of London Bridge and Borough market. Cross the Thames on Southwark bridge and travel up through the City to Hoxton and then on to Columbia Road flower market. Going north, join the Regent's Canal at the south end of Broadway Market, head past Victoria Park and meander through Mile End park, past the ecology centre and over the busy main road on the "green" bridge. Continue down to the Isle of Dogs, close to Canary Wharf, with fantastic views across the river, to the northern entrance of the Greenwich foot tunnel.

Josie Dew, cycling writer

South Downs

A fine rolling saunter is along the narrow, winding lanes that lie to the lee of the South Downs southwest and southeast of Midhurst. While that "ode to a road", the A272, sucks up the vehicles rushing between Petworth and Petersfield, the lanes that twist and turn through such places as Selham, Heyshott, Cocking, Didling, Turkey Island, Quebec, Goose Green, Dumpford, Ingrams Green and the Hartings are comparatively empty of cars. The villages here are and old. Pubs lie around every twist of the handlebars, but there is no finer place to rest a leg and fill a stomach (try the fat fish pie!) than at the historic Three Horseshoes public house at Elsted. In winter the fires are big and blazing, and in summer the spacious garden is full of blooming roses, strutting bantams and tables looking out over the sheep-speckled (at least around Didling) humpback roll of the Downs.

· Sport Relief is the official charity of Bike Week 2008. To take part, go to Sport Relief/bikeweek

· Recommend your favourite cycle routes Guardian.co.uk/environment