I was reading up on what the Islamic State was doing in attacking a city near the Syrian border with Turkey and I discovered a very fascinating location for a Terminal Defense Position. Following the river just west of the city of Kobane, I followed the river into the mountains of Turkey. Once there I noticed an island with an old fortress on it. The fortress of Pertek.
Given its location, the island probably has more history hidden on it than any writer would dream of making up. Sitting smack in the mountains of Eurasia this sort of place is a wonder unto itself.
This is an island located in a lake surrounded by mountains. Can't argue against deep water with steep cliff approaches as benefits. However - in a global wipe out of humanity by zombies being in the connecting land between most major population centers of the planet might be a big downer.
Length of Stay Before Resupply:
Across the lake is ample farmland. If you prepare for it and bring solar panels it is on a similar parallel to my current one making solar electricity very viable. These two supply items would make the stay work quite well.
Farms will work decently for a long while, and being a freshwater lake it is likely to have some decent fishing. However mineral and technical resources are limited in the area - and it won't be an easy trek out of the mountain country to replace things.
This place is a defensible spot with food sources nearby. There is ample sunlight and fresh water would be readily available - as long as no contamination comes from upriver. I think this local with its food nearby makes a solid place to hang out in the apocalypse of undead.
Also - do a Google image search for this area. It is absolutely beautiful. All the good pictures I felt were copyrighted and I didn't want to deal with that issue today.