CONTINENTAL ISLANDS (All of these can be reached by a continental mainland)
Greek Islands: Mitilini, Chalkis, Argostili, Rhodos. NOT Iraklion, Dodekanisos or Nicosia.
Baltic / Öresund Islands: Odense, Kobenhavn, Mariehamn (from two directions), Borgholm. NOT Visby or Ronne.
Sicily
Saishu (Korea)
Hobart (Australia)
ISLAND GROUPS (cannot be reached by continental mainland)---
Canary Island Group
Balearic Island Group
Japanese Islands: All main Japanese islands, along with Naha, Sakhalin Island, Kuril Islands (from Japan).
Indonesian Islands: Java Island Group, Borneo Island Group, Sumatra Island Group, Sulawesi Island Group
Philippine Island Group (not Babuyan)
New Zealand Island Group
Kiska/Amchitka in the Aleutian Islands
Micronesian Island Group
Solomon Island Group
Marshall Island Group
Mariane/Bonin Island Group
I think you can move around the Antilles.
Note that you can not move from Victoria or St. John's in Canada without transports. I'm not sure whether you can walk to San Sebastian in Argentina. I think that's pretty much it.
