London has a secret that its visitors rarely clock until they try it: you can cross the middle of the city from Whitehall almost to Notting Hill and spend nearly the whole time on grass. This walk strings four royal parks together, St James's Park, Green Park, Hyde Park and Kensington Gardens, starting on the gravel of Horse Guards Parade and ending at the gates of Kensington Palace. It runs about six kilometers, past pelicans, palaces, a triumphal arch, a boating lake and a gilded Victorian prince, and it is one of the greenest self-guided walking tours you will find in any capital. The traffic never quite disappears, but for long stretches it is just a hum behind the trees.

Before you set off

Allow about an hour and a half of steady walking, and closer to three hours if you stop to watch the birds, sit by the Serpentine or go inside either palace. The ground is flat almost all the way, with one gentle rise up Constitution Hill, and the paths are paved or firm gravel, so ordinary comfortable shoes are fine. London weather changes its mind several times a day, so carry a light waterproof whatever the forecast says. Mornings are the calmest time, though if you want to see the Changing of the Guard outside Buckingham Palace, check the schedule before you go, because it does not run every day and the crowds gather well in advance. There are cafes, toilets and drinking water points spread through the parks, and plenty of benches. Shade comes and goes: the avenues of plane trees are cool on a hot day, while the open grass of Hyde Park can be exposed. Kensington Palace and Wellington Arch both charge for entry and set their own hours, so check before you go if you want to see inside.

Horse Guards Parade

You are standing on Horse Guards Parade, the great sweep of gravel between Whitehall and St James's Park. Face the long, pale building with the clock tower in its middle: that is Horse Guards, built in the middle of the eighteenth century to a design by William Kent, and the arch beneath its clock leads through to Whitehall, where mounted sentries of the Household Cavalry keep watch. Long before the soldiers, this ground was Henry the Eighth's tiltyard, where knights jousted for the court at the old Palace of Whitehall. Today it is the stage for Trooping the Colour, the ceremony held each June for the monarch's official birthday, when massed ranks of guards in red tunics and bearskins march across the gravel and the King takes the salute. In 2012 the parade ground was turned into a sand arena for Olympic beach volleyball, which still amuses Londoners. Take a moment to look back at the skyline: the rooftops of Whitehall and, on a clear day, the London Eye peeking over them. Then turn your back on the buildings, cross Horse Guards Road into St James's Park, and follow the paths along the lake, heading west toward the blue bridge in its middle, about eight minutes away.

St James's Park Blue Bridge

Stop in the middle of the bridge and turn slowly, because this is one of the best views in London. Look west and Buckingham Palace sits at the end of the water, framed by willows. Turn east and you see a skyline of domes and turrets around Horse Guards and Whitehall that looks almost too romantic to be real, especially on a misty morning. St James's is the oldest of the royal parks. Henry the Eighth took it for a deer park, Charles the Second opened it up and had a long straight canal dug, and in the 1820s the architect John Nash reshaped that canal into the curving, natural-looking lake you see now. The most famous residents are the pelicans. The first ones arrived as a gift from a Russian ambassador to Charles the Second in the 1660s, and the park has kept a small colony ever since. Look for them on the rocks near the eastern end of the lake, preening on the grass or stretching their enormous beaks, and do not be surprised if one strolls along the path beside you. The little island at that end, with its storybook cottage, is Duck Island, and the cottage was built for the park's birdkeeper. When you are ready, leave the bridge on the north side and walk west along the lake path to the palace, about six minutes.

Buckingham Palace

st james park pelicans At the end of the lake, the trees part and you reach the wide open space in front of Buckingham Palace. Find a spot by the railings or on the steps of the white marble monument in the middle and take in the long gray front. That facade is younger than most people assume: the stone face was added in 1913, after the rest of the building had been growing and changing for more than a century. George the Third bought the house for Queen Charlotte in the 1760s, but it was Queen Victoria who first made it the monarch's official London home, moving in soon after she came to the throne in 1837. It was from the central balcony that she, and every monarch since, has waved to crowds on great occasions. Check the flagpole on the roof: the Royal Standard flies when the King is in residence, and the Union Flag when he is not. The monument at your back is the Victoria Memorial, unveiled in 1911, with the old queen seated facing down the Mall and a gilded figure of Victory blazing on top. From here, take the wide avenue called Constitution Hill, which runs northwest with the trees of Green Park on your right, and follow it up to the arch at the top, about ten minutes.