Krachimirsko Vrelo
A spring cave near Belogradchik in north-west Bulgaria. An underground river leads past a rock collapse and a short first sump to Sump 2, which drops straight down. Georgi Mihaylov and I have been pushing it over 7–8 expeditions since 2024. This is our survey of Sump 2, and the cave still goes on.
The cave
01Krachimirsko Vrelo (Крачимирско врело) is a resurgence: the water comes out of the hill and the cave is the river's way in. Getting to Sump 2 takes a walk, a climb, a short dive and a swim before the real diving starts.
- Underground river. From the entrance the passage follows the river that feeds the spring.
- Rock collapse. A breakdown blocks the passage. It's a scramble up and over the boulders on foot, with no ropes needed, then back down to the water.
- Sump 1. A proper sump, fully flooded with no air space: about 8 m deep and roughly 10 m long, surfacing into the next section of river.
- Swim. Another stretch of underground river, swum on the surface.
- Sump 2. The sump pool drops away almost vertically. This is the part we've surveyed: a shaft going down to −46 m, still open below.
3D map of Sump 2
02The passage walls are lofted from the survey's left/right/up/down measurements at each station and coloured by depth. Drag to orbit, scroll to zoom, right-drag to pan. Switch to Profile to see the shaft side on, or Plan to look down it.
The survey
03The plan was to survey with CaveDiveMap. Then the waterproof housing failed and its buttons jammed pushed in, so the phone was no use. At 45 m the wetnotes came out, and Sump 2 was surveyed the old way, with a compass, a pencil and a 50 cm piece of string:
- Heading: compass azimuth of each leg, in degrees from north
- Depth: gauge depth at the station, so each leg's vertical change comes straight from the depths
- Length: distance along the line between stations, counted out in 50 cm string lengths
- LRUD: left, right, up and down distance to the walls at each station, eyeballed
The data runs from the deepest point back towards the surface, the order it was taken on the way out. Depths, distances and bearings are measured; only the wall distances are estimates, so the passage shape is approximate but the line through it is not.
A small Python script walks the legs, places every station in 3D (the horizontal distance is worked out from the leg length and the depth change), then sweeps a cross-section through the LRUD at each station to build the walls.
Side branches and loops are supported. One side passage (station 14 → 88 → 7) closes back onto the main line and misses its station by about 7.6 m, so that loop is a candidate for a re-survey on the next trip.
Station table 27 stations · depth & LRUD in metres
| Station | Depth | East | North | Left | Right | Up | Down |
|---|
Status & next steps
04The cave continues. Sump 2 is still open beyond the end of the survey. We've left the guideline in place with line markers, ready for the next push.
Explored and surveyed by Georgi Mihaylov and me, over 7–8 expeditions from 2024 to 2026.
- Push past the end of the line in Sump 2
- Extend the survey and the 3D model
- Re-survey the 14 → 88 → 7 loop to close it properly, with CaveDiveMap in a housing that works this time
The line in Sump 2 is an exploration line. This is a deep, remote sump past a collapse and a first sump, so it's not a place for an unprepared dive. If you're planning to dive here, please get in touch first.