Updated 19th February 1999; 6th November 2003; 17th November 2007; 23rd October 2009; 30th September 2010; 6th January, 1st October 2011; 4th September 2019; 4th September, 10th October 2022; 11th September 2023

The impressive twin entrances lead to a series of dry, abandoned passages that eventually unite, the way on being through a draughting bedding plane on the left. This passes under several avens before increasing in height at the top of a steep slope. This leads down to water level and a sump. A 10m climb up leads to a chamber with sandstone walls. At the far end, a pitch of 11m drops into an impressive streamway carrying the water from Sima-Cueva del Risco (025). The 1.5km of passage in this area is a three dimensional maze and almost impossible to describe. All ways eventually unite and the way on is in chest deep water up several cascades until daylight can be seen from Torca del Sedo, the entrance to Sima-Cueva del Risco (025). This is an 8m pitch and has been free climbed.
An investigation of draughts in the blockage on the main passage found one from a "small muddy passage low down on the left and other from boulders at the top of the slope. There is at least 10m vertical difference between them. (Logbook 1/8/23)

A dye test in 1964 showed water from Sima-Cueva del Risco resurging after five hours from La Lisa below Cueva de Gonzales (014), Cueva de Transformador (032) and in this cave.

Ortiz in Algunos crustaceous y miriapodas cavernicolas de la Region de Matienzo, Santander (Ortiz E, 1968) describes two male Lithobius, collected in 1966.

The re-survey of the cave in the summer, 2009 by a team from Sheffield University Speleological Society stopped just short of connecting the line with Sima-Cueva del Risco. Surveyed length = 1041m. This was continued during the summer 2010 when the Rosado Series was discovered. The total Tiva length is currently 1882m but there is more to survey. Resurveying continued in the summer, 2011.

The Rosado Series is entered by climbing up from the passage parallel to the main Tiva stream, close to the upstream end. A through bolt is placed to assist with the climb into the tube in the roof of the meander. The meander can be followed to an obvious window on the left wall. This is Carabiner Junction.
Going right through the window leads to small crawls - the Spaniel Series. The left route leads to a 5-way junction - Elephant Junction, with a trunk on the left wall.
Both right hand side branches join and lead to crawls and a final pitch to a too-tight meander. Straight ahead leads into the Chamber of 1000 Meanders. Left leads, via a 6ft stal, to a dodgy climb up into a chamber with a continuing crawl and a hole down that could be dug.
Left at Elephant Junction eventually leads to the Tinto Series. Passages on the right all choke. A pit on the left leads to an aven that could be climbed with some high level leads. Next left leads to helictites and straight on is a way to Tinto, although the route is not obvious.
The Rosado Series appears to be in a different limestone band to the lower series - smooth phreatic passage rather than very sharp limestone.

References: Fernández Gutiérrez Juan Carlos, 1965; Fernández Gutiérrez et al, 1966 (survey); anon., 1974b (logbook); anon., 1974a; Cox G, 1973; anon., 1975a; anon., 1975b (Easter and summer logbooks); Kendal Caving Club and Manchester University Speleological Society, 1975 (survey); Manchester University Speleological Society, 1982 (survey); Mills L D J, 1981; Corrin J S and Smith P, 1981; material in file; Ortiz E, 1968; García José León, 1997 (survey and photo); anon., 2009c (summer logbook); anon., 2010c (summer logbook); León García José, 2010 (Volume 1 and Volume 2) (survey and photos); Corrin Juan, 2011 (See 025 Risco); anon., 2019d (summer logbook); anon., 2022c (summer logbook); anon., 2023c (summer logbook)
Entrance pictures : summer 2019
Underground picture(s): summer 2009 : summer 2010 : summer 2019 : summer 2022
Video: 2022 summer video - All Ages (YouTube)
Detailed Survey : from 1965: low res  high res
from 1975: low res  high res
from rescue site (Risco, Tiva and Oñite)  low res  high res
from 2010: new line and Rosado Series on the 1975 survey. (Updated survey to come).
Line Survey :
On area survey : 1975 Ozana area map. Not a lot of detail. low res  high res
Survex file : 3d file (re-survey, summer 2010) (Amended magnetic declination December 2013 to align with Eur79 grid and coordinates altered to fit ETRS89 datum, April 2014.)
Passage direction rose diagram (Patrick Warren): yes, with Oñite and Risco