It consists of a single shaft, of not too wide dimensions, about 48 metres deep. Here, a large cone of debris forms a pronounced ramp, which reaches the point of maximum depth (elevation – 58). (data taken from the 1934 exploration).

The exploration in March and April 2015 by members of the EC Tortosa and in the absence of a new survey, largely corroborates this description.

The first exploration of the pit took place on 12 August 1934 and was carried out by a group of CEC members led by Lluís Porta i Massana; among the explorers we know that his brother Joan and the biospeleologist Francesc Español i Coll were also there.

We do not have much news of explorations, although we think it may be the same pit explored by the GES of the CMB in November 1958, which they named Avenc d'Ulldecona, they attributed 54 metres of depth to it and they believed they were the first explorers. In 1982 it was also visited by members of the G.E. d'Ulldecona (they called it Avenc dels Arions).

Relocated by the EC Tortosa in March 2015, who proceeded to an exploration, after having to carry out a partial clearing of the entrance.

It should be added that the colleagues from Tortosa detected a fairly important concentration of guilla (what is now called hypoxia) and a strong smell of ammonia from the bats' excrement.

One can take advantage of the excursion and at the finca de l'Arion one can observe a few specimens of the oldest olive trees of the Iberian Peninsula (possibly, they say, from the Ibero-Roman period).

Toponymy: Lluís Porta names the cavity as Avenc de l'Orió (noting that the origin of this name is a corruption of Hilarion). According to official toponymy the correct designation would be Arion, which seems to have the same origin that Porta explains.