At the start of Sunday's Marathon, runners will flash past some of London's most colourfully off-beat sites. Jane Furnival offers a guide
If Marathon runners raise their eyes from the road, they will find some of London's most fascinating secrets along their 26.2-mile route from Blackheath to The Mall.

For slackers, strollers and strayers, here is our guide to everything more exciting than tarmac along the beaten track. If you follow the race on Sunday, remember that it starts at 9am, and roads along the way will be closed to cars at times.

There are three starts to the Marathon course, all on the edge of Blackheath, London's original high-crime area, haunted by 18th-century highwaymen such as Dick Turpin.

The fastest runners take off like a shot along Shooters Hill Road, once the site of artillery practice. Worth a detour is the Pagoda, Eliot Vale, built in 1760 and the scene of Fergie-style frolics by Princess Caroline during her separation from the Prince Regent. Nosey neighbours' accusations of sex marathons with war hero Sir Sidney Smith among others led to a Delicate Investigation by a Royal Commission in 1806. Caroline celebrated her acquittal with a Mediterranean cruise during which she openly slept on deck with her servant, "Count" Pergami.

Back to the modern Marathon. Mass-start runners make their way to Charlton Road past A Gambardella, High Class Refreshments and Sweet Shop, founded by Andrew Gambardella 70 years ago after he arrived from Amalfi, aged 14.

The topiary archway to the former council house No 12 Charlton Park Road wouldn't disgrace Hampton Court. It was created by the late John Clarke 27 years ago.

The older runners start in a quiet street passing the Church of St John the Evangelist, Stratheden Road. The congregation will mumble Marathon prayers for runners at 8am, 10.30am and 6.30pm on Sunday in this Gothic revival gem. In 1853, the Angerstein family picked up the pounds 16,000 tab for the church in the hope that their eldest son would be its first incumbent. Canon Marshall pipped him to the post. His 26-year-old daughter was massacred in the Chinese Boxer Rebellion and has a memorial hall nearby.

Onwards through Woolwich. Eyes left at Depository Road for the rare traffic sign "soldiers marching" near the palatial Woolwich Barracks, home of the Royal Artillery, built in 1758. Their museum is open from 1pm to 4pm, weekdays only, but meander round outside to see the railway gun (made to move on rails) and a Bloodhead Rocket, an airfield defence from the Fifties.

Brave the traffic by Connaught Mews off Grand Depot Road to admire the sun glinting off the golden painting of St George atop the Byzantine ruins of St George's Church. Built as a thanksgiving for our Napoleonic victories, this architectural diamond in the dust was wrecked by a flying bomb on 13 July 1944.

Further along, past the sadly dry fountain and pepperpot towers of the Thirties Woolwich Coronet, you glimpse the river, a futuristic landscape of power stations, steam puffing from silvery chimneys and planes leaving London City airport. Turn off to Leda Road for a prettier riverside walk. Or deviate off Woolwich Road to the Thames Flood Barrier, with a visitors' centre more interesting than it sounds.

You can take a short cut to the Marathon course on the other side of the river via the Woolwich Ferry, created in 1889 and now of Stalinist- workers-style concrete construction. One ferry only operates on Sunday, from 11.30am when roads re-open to traffic.

But if you continue along Woolwich Road into Greenwich, stop to gawp at the plaster busts of Zeus in Chapman Antiques, next to Fingal Street. Or you can buy a disembodied plaster nose for a fiver. Virtually opposite is O'Hagan's Sausage Shop, winner of the 1996 Banger Awards for sausages with "no artificial anything".

Coming into Trafalgar Road, as you pass Christchurch Way, crane your neck for a look at Nos two and three, which boast early insurance signs dated 1695, with painted lions to indicate to firemen that the occupants had paid for protection.

Before you reach the beautiful sweep of Greenwich's Maritime Museum, peep at the fine white stucco frontages of Nos 97-111 Old Woolwich Road. This area's prosperity depended on a special sand mined only from the Woolwich Thames, which prevented iron in clay bricks from reddening.

The Queen's House is the scene of (allegedly) one of the most clearly photographed ghosts ever. A hooded, caped figure extends a bony hand as it creeps up the circular staircase.

If you want to stop, the Fan Museum at 12 Crooms Hill is a Loo of the Year award-winner. For fans of second-hand stuff, the Junk Box, 151 Trafalgar Road, will provide lovable old tat for less than pounds 5.

Next to the famous tea clipper Cutty Sark, another chance to cross to the Isle of Dogs via the Greenwich foot tunnel, opened in 1902 for the benefit of workers commuting to the docks.

Move into Deptford. A bit of a right-on area, this. Malcolm's Up the Creek Comedy Club has proper funny men and four spots available on Sunday night to impromptu joke-tellers. 8.30-11pm on Sunday, pounds 6 entry fee.

Budding Miss Marples will want to deviate off Creek Road to find two mouldering skulls, signifying Tudor skulduggery, at St Nicholas Church, Deptford Green. Here lies the unmarked grave of Kit Marlowe, playwright, murdered on 30 May, 1593. Perhaps en route to Holland to escape an investigation into atheism, Marlowe was stabbed in a drunken quarrel. Killer Ingram Frezer, a servant of spymaster Walsingham, used a 12d dagger and was pardoned four weeks later.

If only Marlowe had known of FA Albin, of 52 Culling Road, off Evelyn Street at the Rotherhithe section of the Marathon route. For pounds 17,500 they will fly you, freeze packed, to store at -197 F in Michigan.

The Rotherhithe section of Evelyn Street inflicts poorly painted street art on its residents. Find a cruelly daubed pub called Loony Toons. Look high. Through the paint, you can just trace its original name, the Harp of Erin, carved in pretty stonework.

Just past the 1903 Fire Station, crane your neck into Blackhorse Road to see a bright blue corrugated garden shed, painted with a mural of a clothes line. Opposite the Pepys Estate is a photomural representing a loo queue, called Waiting To Go, Go, by Sue Evans, 1994.