Between Istanbul and Izmir there are roughly three corridors, and choosing among them is choosing between different versions of Turkey. The western route — about 700 km, three days of driving plus whatever sightseeing you allow yourself — swings west of the Sea of Marmara and down the Aegean coast through Gallipoli, Troy, and the Turkish Aegean islands. The eastern route, the quickest, uses the O-5 motorway through Bursa, Balıkesir, and Akhisar, covering 480 km in roughly five hours non-stop. The central option involves a ferry crossing of the Sea of Marmara before joining one of the overland routes on the south shore.

Each has its partisans. Speed-oriented travellers take the east; history-minded ones take the west. But the western route in particular rewards slowness. It takes in the Gallipoli battlefields and cemeteries, the Dardanelles narrows, ancient Troy with its fine adjacent museum, the Troad Coast with its landscape of boulders and dryland vegetation, and the beach resorts of the Gulf of Edremit before approaching Pergamon and Izmir's outer suburbs.

Heading west out of Istanbul, the first hundred kilometres are industrial — automobile factories, cement works, and suburbs without end. The scenery arrives later. Tekirdağ, 145 km from Istanbul, has beach resorts and ferry connections to the Marmara Islands. South of Gelibolu, the road reaches the Gallipoli Peninsula, where the 1915 campaign of World War I left battlefields, cemeteries, and monuments still visited by hundreds of thousands of Australians, New Zealanders, and Turks each year. The campaign never progressed as far north as Gelibolu itself; the fighting — and the dying — happened at the strait's narrowest point, near Eceabat and Kilitbahir.

From the peninsula, ferries cross the Dardanelles to Çanakkale, the area's main city, before the road turns south toward Troy. The ruins are described as modest, but the museum built beside them is outstanding. A few kilometres south, the Troad Coast road branches off toward Assos, a hilltop temple, and a series of beach resorts before rejoining the main highway near Küçükkuyu — east of Assos, and not far from the ancient city of Antandrus on Devren hill.

Edremit, 480 km from Istanbul and 200 km short of Izmir, sits at the inland tip of the Gulf of Edremit — the ancient Gulf of Adramyttium. The town is backed by Mount Ida, known in Turkish as Kazdağı, which rises to 1,774 m and was, in Greek mythology, the grandstand from which the gods watched the Trojan War. Its southern slopes are a national park. The foothills below are dense with olive groves, and the towns along the gulf shore — Altınoluk, Akçay, Burhaniye — are beach resort towns with some of the best swimming on the itinerary.

Just inland are hot springs, particularly at Güre, and the ruins of Astyra. On the hillside above Avcılar and Altınoluk sits the ancient city of Antandrus. The main highway continues to Ayvalık, a pretty town of cobbled streets and neo-classical churches, before the Pergamon turn-off arrives. The ancient acropolis at Bergama needs several hours; many visitors find the carpet shops need rather more.

The eastern motorway route through Bursa has charms of its own, though they are different in character. Bursa, 155 km from Istanbul, was the first Ottoman capital — a UNESCO World Heritage Site with antiquities scattered through an otherwise busy modern city. The mountain immediately south, Uludağ, becomes a ski resort in winter and a kebab-eating destination in summer. From Bursa the highway continues south through Karacabey and Balıkesir, a large modern town where the railways from Bandırma and Eskişehir converge.

South of Balıkesir, the ancient site of Thyatira (modern Akhisar), one of the Seven Churches of Asia addressed in the Book of Revelation, offers a diversion before Manisa — the last major stop before the Sabuncubeli Pass and the descent into Izmir's coastal plain. The eastern route trades spectacle for efficiency, though Sardis, the capital of the ancient Lydians with its extensive Graeco-Roman ruins, is a worthwhile detour east of Turgutlu for anyone with a car.

The best seasons for this journey are April to mid-June and September to late October, when the fruit trees are in blossom or the vineyards are ripening and the weather has not turned scorching. Turkish buses are frequent, comfortable, and inexpensive — airline-style seats, free drinks, and charging points are standard. The western coastal route is more constrained: buses run frequently as far as Çanakkale from either end, but only one service a day runs the full length through to Izmir. Renting a car gives maximum flexibility, though you will need an HGS electronic toll tag included with rentals.

The corridor is also served by trains between Istanbul and Izmir, which take roughly twice as long as buses but pass through different scenery. Night trains connect Istanbul with Sofia and Bucharest; a summer car-train runs from Villach in Austria to Edirne. Whatever the mode, the guiding principle is the same: the itinerary between these two great cities is not a transit corridor. It is a destination in itself.