This expansion is the only professionally produced expansion NOT to be produced by Games Workshop (or licensees of Talisman.
Jaskinia or the Cave, adds a new board to the game along with a new deck of cards to encounter.
It is thought to be a very difficult expansion as many of the enemies within the Cave have very high scores for Might or Magic.
It seems that the production of this expansion brought about an end to relations between Sfera and Games Workshop, as the license was revoked shortly after this.
Sfera went on to produce a Talisman-esque game, Magiczny Miecz.