Karst all around, Trieste

From downtown Trieste you can take the funicolar tramway (buy 1 hour transport ticket, 1 euro) and in 20 minutes reach the highland (400 mts. above sea level) with terrific panorama and a scenic route. From the tramway station above in Villa Opicina ( with the same transport ticket) you take the bus 42 (10 minutes) to the Giant Grotto, in the Guinnes book of records as the greatest touristic cave of the whole world...( ticket 8 euro with guided tour every hour included )

A very romantic way to get to the Carso above Trieste would be on the old funicular tramway that runs up from Piazza Oberdan in the city centre along Scorcola hill to the town of Opicina on the plateau. The ride offers splendid views of Trieste and the Gulf.
Unfortunately it doesn't work from the 1st of June. After 20 years they are updating the new techniques for the funicolar plants.

Guinness Book of Records as the largest accessible cave in the world.

Unfortunately I did not have time to venture out this way, but from the pictures I’ve seen, this is something I wish I could have done.

special thanks to Micky (aussie75) for providing me with helpful info to provide you with.

Before cultural forces gave Trieste its social form, of course, there were geographic elements that gave it its physical form. The Grotta Gigante, listed in the Guinness Book of World Records as the largest cave available to tourists, was inhabited during prehistoric times. With its massive domed vault, it could easily accommodate St. Peter's Basilica. Two white plastic tubes in the center of the grotto are part of a scientific experiment measuring the tides of the Earth. (It appears that it is not only the sea that rises and falls with the movement of the moon; that the Earth also expands and contracts with the lunar pull is being studied here.)