St. Philip and James's cave, or Grotto, is situated on the southeastern slope of the Plića hill and it is elliptical in shape, about 62 meters long, and not more than 19 meters wide. It is divided into two main rooms: the first consisting of an aligned part, 22 meters long and 12 meters wide, with two built-in slopes, and the second one, lower, and unlit. In the main axis, the cave is oriented north - south, with the entrance arch to the south. During daylight, the ambiance in the cave is still mystical, just as it has been to people since prehistoric times. The entire cave has been converted into a sanctuary because of the chapel and the altars located in it. The central space is dominated by the chapel of St. Philip and James, whose external length is 4 meters and width 3.4 meters, with walls 65 centimeters thick, and a roof leaning against the arch of the cave. The chapel is dedicated to the apostles St. Philip and James, whose cult is still preserved in this area, especially that of St. James, after whom the parish church was named. Next to the chapel, there are six masonry altars, separated from each other and freely located in the space, which, according to legends, belonged to one of the villages of Marina. In addition to the chapel and the altar, the room also has a masonry tomb and two large wells. Above one of them is an inscription written in the Gothic script from the 14th century: „MAGISTER JACOBUS DE VENECIS ME FECIT“ (The craftsman Jakov from Venice built me). Today, in front of the cave and in its surroundings, you can find the remains of ancient walls and medieval tombstones (stećak). A portrait carved on the left pillar at the entrance to the cave belongs to the ancient period. We can add the drawings of the Archangel Michael with wings and an orb with a cross, and the figure of a dragon swallowing a creature to the early Christian period, as well as numerous inscriptions and crosses. The cave is a kind of archive of literacy with graffiti in stone, in which the Latin alphabet, Gothic italic alphabet, ornate letters by craftsman Jakov, and the Bosnian Cyrillic alphabet are intertwined, right down to the latest inscriptions that ruthlessly cover those much older ones.
Today, as in the past, many pilgrims from the central Dalmatian area gather in the cave on the holiday of St. Philip and James (May 1st). On the level of the chapel of St. Philip and James, a tour of the cave would begin, from left to right. This tour was called - the tour of the Holy Circle. At the bottom of the cave, people rolled over on a large stone panel called the tomb of St Magdalene (Sv. Magdalena) to prevent gout and infertility. In the immediate vicinity of the tomb of St Magdalene, there was a path to the so-called Prometalo (interception) - a group of three stalagmite pillars, where the custom of passing between the pillars was performed. If someone could not get through it was a sign that the person committed a lot of sin the previous year. The story of how St James drove out the peasants with their cattle and ordered them to build his temple there is related to the cave as well. There are stories of buried treasure also associated with the cave. The mythological origin of those stories can be found in the Argonautica and the golden tripod left to the Hili people.
Mass and pilgrimage are traditionally held there on May 1st.