Alonissos has a number of offshore islets that are a favourite day-trip destination by boat. Set in the marine park and as island nature reserves in their own right, some have restricted access to the public.
Peristera, the scarcely inhabited islet easily seen offshore on the east coast, was once joined to Alonissos and is graced with some beautiful sandy beaches that are usually empty. The place is a favoured haunt of barbecue boats in the high season, and a cantina sets up on the main beach. Recently underwater archaeologists discovered an ancient wreck off the island.
Pelagos or Pelagonissi is also sometimes called Kyra Panagia after the monastery that lies to the east. It is a hilly islet with two deep bays.
Gioura is dramatically rocky with precipitous cliffs and is specially protected as its underwater caves are the primary habitat of the Monk Seal. It also harbours a rare species of wild goat and a remarkably beautiful cave in the interior, reputed to be the original dwelling of the mythical Cyclops.
Psathoura is small and flat with the remains of an ancient city sunk beneath the waves to the east. In the north is a large lighthouse, built in the last century by the French.
Piperi is usually closed to visitors as it is one of the most critical of habitats for the Monk Seal, Eleonara's Falcon and several rare plants. Piperi has a steep rocky shoreline.
Skantzoura is a favourite anchorage for yacht flotillas. The islet has a series of low hills on shores of white marble that create a dazzling azure seabed along the shoreline. There is an abandoned monastery at its centre.
The National Maritime Park of Alonissos was the first to be set up in Greece and comprises Alonissos and six smaller islands as well as uninhabited rocky outcrops. The area is an essential habitat for many species of fish, birds, reptiles and mammals including the Mediterranean Monk Seal (Monachus Monachus) which has the unfortunate distinction of being one of the rarest animals in Europe.
The Biological Station at Gerakas Bay, on the northern tip of the island, has been regarded as an embarrassing white elephant since the day it was completed in 1985 with a generous dollop of EC funds. The station has remained virtually unused, hosting just four official functions, one of which was its own opening ceremony.
Now the much-maligned building, which looks just like a holiday villa, may act a forward base for research and there are plans for a marine park centre in Gerakas itself. It took 25 years to get the park established and, after another 20 it still had no plan, no staff, no authority and, so some claim, no hope of success. It has a website though at Alonissos Park.