List of Huts and Campsites
For the same list but maintained by a comunity, check: https://nomadwiki.org/en/Wilderness_huts
Czech Republic and Slovakia are the most densely covered on this site, quite a lot can be found in Austria or Italy as well. Curiously, they include a list of shelters in Nepal and huts in Finland. The listings are sorted by types, each includes a brief description, a list of equipment, a map of surroundings, information about water source/supply, way of access and the most convenient visit time.
Similar to the website above, in German about some mountain huts in the world.
They are referred to as 'bothies' within the UK. Most of these bothies are in Scotland under the care of the Mountain Bothy Assoication(A voluntary run organisation who maintain these shelters). You can find these bothies by checking their website.
"They are referred to as 'shelters'. There are many within Denmark and there are two useful resources for finding them. The first is the website. The second is a free mobile app called 'Shelter'. It's in Danish and pinpoints the locations of the shelters on a map and provides general info on each one."
AUSTRALIA, NEW ZEALAND, CANADA, USA & UK
WikiCamps apps are maps with pinpointed locations of free designated camping areas which have varying facilities. (free trial with Android; I believe it costs with iOS)
This site was recommended. In Russian (needs checked as couldn't translate)
"Basic free designated wild camping areas in the Netherlands - not accessible by car only by foot/bicycle, max. 3 tents. water available."
Shelters in Sweden
"In Estonia we have two types of shelters: houses and huts. First ones require "key money" and booking, although the huts are free, and you have to make room for everyone who wants to stay there aswell. Most of them should be visible on this site."
Here is a website where people are adding the information they find about shelters and also water points etc..however its only in French. Since it is located in maps that is very easy to understand. Generally, the "refuges non gardés" are the free ones. There are infos about other countries as well. But I guess that is not very complete since travellers themselves are filling the infos
List of free mountain huts in Andorra.
Here is a map of ALL of the mountain houses, cabins, huts, shelters, and refugios in the Balkans and surrounding areas(Including Slovenia, Croatia, Bosnia, Serbia, Montenegro, Greece, Macedonia, Bulgaria). Some are free and wild or very remote, and some are touristic and you must pay to stay or call ahead, so check the info pages carefully."
Map of free camping, hot springs and huts in Japan.
(yellow spots are campsites; free or very cheap. Clicking on the dot on the map opens the campsite info page, the ones with a blue semicircle saying 無料 are free, the ones with a red semicircle saying 有料 are not)
A map pinpointing 12 free huts in Canada.
"you can see a number of very simple, mostly open shelters in different areas of Germany. Look for articles starting with Schutzhütten to see huts listed with GPS-coordinates. (In German)"
Mountain huts and refuges of the Sierra Nevada
(as well as various other countries)
Map indicidating free shelters
This site includes info on free wilderness huts in Finland.
Free camping spots in Belgium.