Though generally quite a dry island, Syros is visited mostly for its beaches and marvelous and cosmopolitan harbor town of Ermoupoli, which was Greece's main port during the 19th century (till the 1890s).
A National Historical Landmark, the town is spread out over the slopes that rise from the water, with two hills, one with a Catholic quarter, from Venetian and Genoese times, the other the Greek Orthodox quarter from War of Independence times, with long flights of steps leading up to both. Along the waterfront and back in are beautiful ship builders' mansions, impressive paving stones everywhere, lovely square with neoclassical buildings and cafes, and fine churches. Many of the fine buildings were designed by architects from France and Germany.
Syros is famous for its loukoumi (known elsewhere as 'Turkish delight'), and is in general a big shopping island, visited by many who come just to shop, where one can find just about anything (by Cycladic Island standards) in the many shops.
Apart from its obvious elegance, Ermoupoli is one of the most industrialized towns in all of Greece, with cotton and textile mills, wrought iron factories, tanneries and ship yards; its Neorion floating dock, built by shipping magnate Goulandris, gave the port a boost after WWII.
On the cultural side of things, the marble paved square, Platia Miaoulis has an 1878 Town Hall, the Apollo Theater, copied from Milan's La Skala, a public library, many cafes, with an impressive clock tower nearby; the archaeological museum houses prehistoric finds from Paros and Syros from the 3rd millennium BC; the Orthodox Metamorfosis cathedrdal is near here.
Up the hill, the Ayios Nikolaos church, dedicated to the island's patron saint, has a carved marble iconostasis by 19th century sculptor Vitalis, and a blue and gold dome. The Monument of the Unknown Soldier (the world's first), with a wonderful stone lion also by Vitalis on top of it, sits in a little grassy area just below the church.
The neighborhood of Vaporia with fine ship builders' mansions is off to the right of the church, below which are four town beaches below flights of marble steps. In the Orthodox quarter of Vrondado, uphill from the clock tower in the main square, the church of the Anastasi has some icons, and fantastic views from its terrace; the area's narrow lanes a pleasure to wander in, with big squares paved in marble, fine mansions, and some good tavernas on the steps.
Ano Syros, the 13th century Catholic quarter, is 870 steps up from the port, though buses go there for those reluctant to climb them. A short cut leads up from the stepped street of Andrea Karga. The area, off bounds to cars, and boasts many churches (including an Orthodox cathedral), the British Military Cemetery (from World War I), a 16th century Capuchin monastery, founded as a poorhouse, a Byzantine museum, an 18 century Jesuit cloister, a women's handicrafts cooperative, a cultural center, the radio station, and the Markos Vamvakaris museum, Vamvakaris the main figure in the 1930s rembetika music scene, viruostic bouzouki player and gravelly voiced singer, born on Syros.
The rest of Syros has its greenest areas on the west coast, with some produce, including dairy products; there are good marked hiking trails, remains of an old settlement at Kastri, and good beaches, some of which are remote and unspoiled; Galissas beach, in the south, is nice but gets very crowded in season; there are two campsites there, and nude bathing at nearby Armeos beach.