Sifnos is one of the six islands making up the Western Cyclades. It's roughly the same size as Serifos or Santorini, and with a year-round population of less than 3,000 people. It's made up of three main villages, the capital being Apollonia, where about one-third of the island's population lives.
Sifnos has no airport but is well-served by ferry connections. Its nearest large neighbours are Serifos to the northwest, less than a half-hour by ferry; Milos to the southwest (30-60 minutes on the high-speed ferries, around two hours on regular ferries); and Paros to the east, which is a little bit further and slower, taking about 5 hours 25 minutes.
Other ferry connections include Piraeus (2-4 hours high-speed, otherwise about 5 hours); Santorini (2.5-3 hours high-speed, 5-7 hours regular ferries); and Mykonos (6-7 hours).
Many of these ferries operate on a daily basis in summer, though some are only a few times a week so always check.
Ferries in Greece has an excellent and very thorough website where in addition to checking ferry schedules and times, you can also book tickets and get lots of useful information about travelling by ferry in Greece.
Sifnos is mainly good for hiking, sunbathing and swimming. There are a number of excellent tracks all over the island, with maps available locally. Many of these tracks lead to isolated churches and monasteries, which are visually striking in their remote settings.
Beaches tend to be quiet, apart from a few small resorts. You won't find watersports, and probably no place to buy snacks or water, so go well-prepared.
In Apollonia there is a small Folklore Museum, and the island's Archaeological Museum is in Kastro. Probably only of interest to specialists is an Ecclesiastical Museum at the Monastery of Panagia Vrysiani near Exabela.
Sifnos has several small archaeological sites and ancient ruins around the island too, which also add to the pleasure of hiking here.
Apollonia is probably the best bet if you want to be somewhere lively (by Sifnos standards). You can set off on several hiking trails from here, and explore further on the local bus that runs through the town. In the evening there's a good choice of eating options. It's also very photogenic, with lots of narrow and winding traffic-free streets.
Kamares is the port of Sifnos, and can also make a good base as it has more of a beach resort than a typical Greek port atmosphere. It's also where you'll find the local tourist information office.
The hilltop village of Kastro used to be the island capital. It's one of the most picturesque spots on the island, with whitewashed houses, narrow streets, blue-domed churches and an ancient wall running around it. There's less choice of accommodation and eating places but you'll have a truly wonderful island experience if you base yourself here.
This Athens dining guide doesn't list restaurants but gives practical advice on types of eating places, tipping, hotel breakfasts and picnics.
Spetses in the Saronic Gulf Islands of Greece is an easy day trip from Athens and has some good beaches. This page gives details of ferries and what to do.
Athens Airport hotels include the luxury Sofitel at the terminals, Holiday Inn near the airport, and others close by like the Hotel Pantheon.