Research trip to Torhola

In June, the caving association did a combined research & training trip to Torhola cave in Lohja - Finland's largest limestone cave. The event was a in-cave training part of our basic caving course held by Ralf Strandell, the in-cave training was by Dare Talvitie, Jaakko Jääskeläinen and Jarmo Ruuth, with five trainees (youngest was three). Jari Arkko was testing a new spatial information application that pinpoints where the cave is underneath on the map when you walk in the environment. Jari and Taina Nyman also scanned Torhola's two side caves. We also observed flora and fauna in the cave.

That's a lot! Let's start unpacking the above with the new application. Jari had developed an application that can take as input cave coordinates, cave 3D models, and the orientation of those models with respect to the coordinate system. 

The application is used on the surface, and can then pinpoint in real time on a map display where the underlying caves passages are in relation to the user's position. This can be useful to understand where the cave is. It could reveal, for instance if there's any chance of finding additional entrances or points of the cave that are near the surface.

This is early work and needs further development. One of the issues observed during the test was the accuracy of GPS positions in phones. We observed +- 10 meter fluctuations, particularly in an area with foliage and cliffs. Similarly, the accuracy of the recorded cave coordinates and which part of the cave they point is an issue. There's also a need to obviously have either a 3D model or a plan view map to do this, and those need to be oriented in terms of their compass direction, altitude, and where on the map the published cave coordinates are.

Here's an example of using the system in its current state, with the blue dot showing where the user is and the black drawing indicating the outline of the cave underground.

Then to the training. This seemed to go very well, with some of the most eager cavers entering the lower tunnel from the basement of the Torhola cave from the outside. There's a rock blocking going to the actual cave, but we have not seen people go into this extremely small hole this far before. The hole is so small that only the people with thinnest bones can actually enter. Helmets, for instance, cannot be worn when entering, and even those who can enter need to twist and turn their body to go in. Well done!

What the small tunnel looks inside is shown in the opening picture of this article.

Here's a picture of what the entrance looks from outside:

Then to the scanning exercise. There are two side caves of the main Torhola cave, which we call Torhola 2 and Torhola 3. Their coordinates are N 60.252333 E 23.857586 and N 60.252292 E 23.857464, respectively. Torhola 2 is right behind the main cave and is small, the 3D model says 7 meters but some of that is probably not something a human can enter, the cave gets very low. Torhola 2 is larger and quite interesting to explore. The 3D model says 16 meters long, a dogleg shaped cave. The entrance is a crack that allows you to drop down to the cave.

Here is Taina scanning Torhola 2:

The Torhola 2 map can be seen in high-resolution here, the model downloaded here, and rotated in your browser here.

The Torhola 3 map can be seen in high-resolution here, the model downloaded here, and rotated in your browser here.

And here are the resulting 3D models and maps:

Finally, we looked especially carefully in Torhola 3 about if we can spot any living things or traces of them. The main occupants seemed to be spiders, of which there were plenty. The brave explorers in the lower tunnel of the main cave reported seeing many spiders there as well. 

In Torhola 3 there were also big roots growing through the floor of the cave and signs of organic material such as oak acorns/nuts.

Here are some pictures of the team looking Torhola 3, roots, and nuts, and spiderweb:

The cave is well marked, one of the most well-known caves in Finland. And a protected area. There's a parking lot with a sign pointing to the short trail leading to the cave:

This article has also been published at Planetcaver.net here. Read the full Planetskier series at planetskier.net, urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net, or all blog articles from Blogspot. Photos and text (c) 2026 by Jari Arkko, Jarmo Ruuth, and Taina Nyman. All rights reserved.