The White Mountains is in a sense the story of a thousand-kilometre walk, and begins in "Wherton", an imaginary village on the first of many rivers in the trilogy. (Will is a miller's son and has always lived over the river.) "Wherton" lies north of the Hampshire town of Winchester, and some way west of Alton. Jack has been south, visiting an aunt at Bishopstoke (traditionally a possession of the Bishop at Winchester, hence the name):
"I went out one day, walking, and I came to the sea. There were the ruins of a city that must have been twenty times as big as Winchester." [...] "...I saw something there. It was the hulk of a ship, rusting away..."
The city is Southampton, home port of many passenger shipping lines. In Chapter 3, the travellers follow the tops of the South Downs, a narrow line of chalk hills given over to sheep grazing: the Downs pass through Winchester to the south coast, then run alongside the sea between Worthing and Eastbourne. The harbour town of "Rimney" is, according to Christopher, intended as New Romney, where curiously enough he later moved to live. The crossing in Chapter 4 is a long one, about twenty hours under sail, to a landing 150 miles north-west of Paris: perhaps Le Havre or Dieppe.
In Chapter 5 Paris is unmistakeable, as is the Isle de la Cité, ancient centre of France, and its cathedral Notre Dame:
There had been twin towers in front, but one of these had been sliced down the side. On them, and on the whole façade, were carvings in stone, and from roofs and angles stone figures of monstrous animals probed the quiet air... The huge wooden door stood open, tilted on its hinges and rotting. Part of the roof of the nave had fallen in, and one could see up past the pillars and buttresses to the sky.
The travellers leave Paris by the "wide river, flowing south-east", the Seine, and in one long day's walk and a horseback ride reach a confluence, on the western side of which is an ancient chateau. Chapter 6 is thus spent near Fontainebleau, home of the Kings of France and of Napoleon, built in many stages over the centuries and with both a fishing-lake and a field once used in annual Tournaments of chivalry. Christopher uses the name "Chateau de la Tour Rouge", which seems to be built of red brick. In Chapter 7, Will fords the southern fork of the river (at Moret sur-Loing) and rides south-east out of cultivated land and through the hills of the Bourgogne: in Chapter 8 the travellers follow and then abandon a canal, and:
At last we looked down from the hills into a broad green valley, through which a great river flowed. Far in the distance, other hills rose. Beyond them again, according to the map, were the mountains which marked our journey's end.
The valley is that of the Saône, which they swim, and the "other hills" lie toward the south of the Jura region. This leaves only, in Chapter 10, the "Great Lake" (Lac Leman), a broad plain around Lausanne and foothills rising to the White Mountains, i.e., the Bernese Oberland chain of the Alps. Their final destination is described unambiguously in the last pages of The White Mountains: the Tunnel is the railway tunnel slanting up through the Eiger glacier from Eigergletscher below to the Jungfraujoch observatory, at 3580m altitude, above. A more spectacular refuge is hard to imagine: the topmost point of the hub of Europe.
[The Observatory, with the summit of the Mönch behind and all Europe below. The final scene of the trilogy is set on the plateau of snow just behind, by the trail of footprints.]
Further confirmation is given in Chapter 1 of The City of Gold and Lead:
...there was a big house at the top, and a building with a domed roof of metal that had a vast telescope pointing at the sky, and a cave where strange figures were carved from the ice.
The cave is a gallery of ice-sculptures and the observatory is called the "Sphinx": it's still used by the University of Liège for solar physics astronomy, and by the Swiss Meteorological Office for climate research.
[The Jungfraujoch railway, close to the lower entrance of the Tunnel: location of the opening scenes of The City of Gold and Lead]
In Chapter 2, the expedition passes down through Lauterbrunnen, crosses Interlaken and skirts the western lake before heading north for a hundred miles to a ruined great-city encompassing a bend in the river, which flows from east and turns to north. This can only be the Rhine, turning through Basel, and in a nearby town the barge is joined. Wurtemburg lies downstream to the north, from which the raft-trip passes through two ruined cities, perhaps Karlsruhe and Mannheim. Mainz and other ruins are crossed by rowing-boat.
The Games, in Chapter 4, are held at a town in windmill-country with a twin-towered church and Roman remains of an amphitheatre: where there is a legend of an ancient and terrible battle. This might be Cologne/Köln, where France, Germany and Holland meet, the most important Colonia (regional capital) in the Roman Empire west of the Rhine; and captured on 5 March 1945 by the U.S. 104th Infantry Division after terrible bloodshed. But a local correspondent suggests that perhaps it is not Cologne but the other Roman colonia at what is now the small town of Xanten, where the countryside is more windmill-filled, and where a fine amphitheatre survives; the battle might then be a reference to the reconquest of Germany by the emperor Augustus, which began from here.
In Chapter 5, the Tripod sets out and fords the Rhine here only to travel back south to an especially ugly ruin, Koblenz, at a river fork: the City thus lies across the Mosel near where it meets the Rhine.
In the trilogy's third book, The Pool of Fire, the journeys scale up to match the world-wide proportions of the struggle: but, as we shall see, the geographical style continues both vague and precise.
Chapter 1 takes place in once-electrified limestone caves under wooded hills "a long way to the east [of the White Mountains, i.e., of Interlaken in Switzerland], in hilly rather than mountainous country". The Hallstatt caves, in Austria, seem plausible.
Chapter 2 is the narrative of a year-long journey of some two thousand miles, establishing one of the long lines of communication needed by the rebels. Here goes: the journey crosses a pass southeast through to north-east Italy ("a rich plain"), the shores of the Adriatic ("a sea that beat, dark and tideless, against rocky shores and little fishing harbours"), east and then south through Croatia and Serbia ("with hills and distant mountains on our right hand"), crossing the mountains of Macedonia back west into southern Greece ("Hellas"); then east around the Aegean sea to Istanbul ("an isthmus between two seas, near which stood the ruins of a great city (it was relatively little overgrown with vegetation, but looked far more ancient than any other we had seen)") and on into Turkey, across desert ("on the edge of a great desert and a long way from habitation") as far as "a broad warm waterway which moved in sluggish serpentine coils through a green valley": we are now probably in northern Iraq or Syria, and the river is either the Tigris or the Euphrates. The return journey is "different", through a pass in the Caucasus to the "eastern shore" of the Black Sea, somewhere near Batumi in Georgia, then "round, to the north, and west" into the Ukraine, where "the people spoke the Russian tongue", further west across Hungary and then along the Danube: "For many days we had been following a vast river, on which ... much traffic plied." The ruins of another great city, Vienna, are skirted and the main event of Chapter 2 -- the Hunt ritual -- is witnessed in a town above the ruins, high on the west bank. (Vienna because the scene is only "a few hundred miles" from the caves; the river flows away "into an autumn sunset", i.e., west, ruling out Zagreb and Budapest; and the local currency is groschen and schillings, suggesting Austria.)
In Chapter 3, the research base, the castle, is introduced. It lies two long days' hard riding westward from the caves and on a fishing coast running north for at least fifty miles (since the pit is dug fifty miles north up the coast): also, Chapter 7, there are rough hills inland; and, Chapter 9, laboratories in France are "not far" away. The most reasonable location is somewhere near San Remo, north of Monaco, on the French side of the Ligurian Sea (the gulf between France and Italy). Monastic forts abandoned since the Middle Ages do indeed exist on the coast here though the most famous example is further west (near Montpellier).
The Atlantic voyage in Chapter 8 departs from "a port in the West of France" in the Bay of Biscay (La Rochelle?), as Henry's earliest voyage had in Chapter 2. (Henry makes at least three Atlantic crossings in the book, forging links to the City in the west, much as Will and Fritz do toward the East.) The ship passes the Caribbean islands to arrive at a secondary base a hundred miles northwest of Panama, just into what is now Costa Rica.
The West City is at the Panama Canal (see above), and the only information as to the East is given in Chapter 8 of The City of Gold and Lead:
...both well to the south of this one and situated far apart, one on the edge of a great continent to the east, the other on an isthmus between two continents to the west.
The east City must be on the outflow of a great river into the China Sea, and if it shares the southern latitude of the west City then perhaps the Mekong, flowing out of what is now Cambodia.