120 m² cave in First World War base XVIII:10 in [Krepost Sveaborg](https://en.wikipedia.org/wiki/Krepost_Sveaborg) land front defense line in Kasemattikallio park, Maununneva, Helsinki, Finland. The base was built in 1915 - 1918. The cave connects the trenches betwee western and eastern parts of the base.
The whole base contains:
* 150 meters of thrench
* 2 observation positions
* 2 search light positions
* At least 5 shelter rooms
* 120 m² cave
More info:
* [Location in Google Maps](https://goo.gl/maps/jgmBfQrNAeF5RhnB6)
* [Wikipedia: Krepost Sveaborg](https://en.wikipedia.org/wiki/Krepost_Sveaborg)
* [John Lagerstedt , Markku Saari: Krepost Sveaborg](http://www.novision.fi/viapori/eavaus.htm)
* [Finnish Heritage Agency site info](https://www.kyppi.fi/to.aspx?id=112.1000013737) (only in finnish)