Wo befindet sich dieser "wayside shrine". Hier ist nur ein Stein mit einer verblassten Aufschrift.

The lake contains a big island, which is not visible in the regular OSM (only that there is a forest when you zoom in). In the editor it is visible, that obviously the island was done by its outlines, but not treated in the right way or with the right attributes. In my opninion it needs an experienced mapper to solve this problem. Furthermore, on the island are lots of trails, panoramic views, picnic sites etc. which need to be shown. The person, who will go there to do it, will be rewarded by a stunning landscape ;-)
One more thing: on the lake is a boat line connecting the island with the town but also some other points around the island.

What type of building is this?

大島

wikidata=Q137971923

中島 (Nakajima) is the name of the island group (see https://ja.wikipedia.org/wiki/中島_%28洞爺湖%29)

弁天島

wikidata=Q137884305

観音島

wikidata=Q49645323

大黒殿

wikidata=Q137884853
wikimedia_commons=Category:Shinto shrine Nakajima Island (Lake Toya)

饅頭島

wikidata=Q137884306

Irgendwo hier sollte das Karl-Münichreiter-Denkmal sein