The 1st-century BC Tombs of the Patriarchs.
The compound is the second holiest site for Jews, (after the Temple Mount in Jerusalem) and is also venerated by Christians and Muslims, both of whom have traditions which maintain that the site is the burial place of three biblical couples: (1) Abraham and Sarah; (2) Isaac and Rebecca; (3) Jacob and Leah. According to the Midrash and other sources, the Cave of the Patriarchs also contains the head of Esau, and according to some Islamic sources it is also the tomb of Joseph. Though the Bible has Joseph buried in Shechem (the present-day Palestinian city of Nablus), Jewish aggadic tradition conserved the idea that he wished to be interred at Hebron, and the Islamic version may reflect this. The Jewish apocryphal book, The Testaments of the Twelve Patriarchs, also states that this is the burial place of Jacob's twelve sons.
The more visible known entrance to the caves.
The caves under the enclosure are not themselves generally accessible; the waqf have historically prevented access to the actual tombs out of respect for the dead. Only two entrances are known to exist, the most visible of which is located to the immediate southeast of Abraham's cenotaph on the inside of the southeastern section. This entrance is a narrow shaft covered by a decorative grate, which itself is covered by an elaborate dome. The other entrance is located to the southeast, near the mihrab, and is sealed by a large stone, and usually covered by prayer mats; this is very close to the location of the seventh step on the outside of the enclosure, beyond which the Mamelukes forbade Jews from approaching.
When the enclosure was controlled by crusaders, access was occasionally possible. One account, by Rabbi Benjamin of Tudela dating from 1163 CE, states that after passing through an iron door, and descending, the caves would be encountered. According to Benjamin of Tudela, there was a sequence of three caves, the first two of which were empty; in the third cave were six tombs, arranged to be opposite to one another.
These caves had only been rediscovered in 1119 CE by a monk named Arnoul, who had noticed a draught in the area near where the mihrab is at present, and had removed the flagstones and found a room lined with Herodian masonry. Arnoul, still searching for the source of the draught, hammered on the cave walls until he heard a hollow sound, pulled down the masonry in that area, and discovered a narrow passage. The narrow passage, which subsequently became known as the serdab (Arabic for passage), was similarly lined with masonry, but partly blocked up. Having unblocked the passage, Arnoul discovered a large round room with plastered walls. In the floor of the room, he found a square stone slightly different from the others and, upon removing it, found the first of the caves. The caves were filled with dust. After removing the dust, Arnoul found bones; believing the bones to be those of the Biblical Patriarchs, Arnoul washed them in wine and stacked them neatly. Arnoul carved inscriptions into the caves describing whose bones he believed them to be.
This passage to the caves was sealed at some time after Saladin had recaptured the area, though the roof of the circular room was pierced, and a decorative grate was placed over it. In 1967, after the Six Day War, the area fell into the hands of the Israel Defence Forces, and Moshe Dayan, the Defence Minister, and an amateur archaeologist, attempted to regain access to the tombs. Dayan, not knowing about the serdab entrance, started investigating the shaft visible beyond the decorative grate and came up with the idea of sending someone thin enough through the shaft and down into the chamber below. Dayan eventually found a slim 12 year old girl named Michal and sent her into the chamber with a camera.
Michal explored the round chamber, but failed to spot the stone in the floor that led to the caves. Michal did, however, explore the passage and find steps leading up to the surface, though the exit was blocked by a large stone (this is the entrance near the mihrab). According to the report of her findings, which Michal gave to Dayan after having been lifted back through the shaft, there are 16 steps leading down into the passage, which is 1 cubit wide, 17.37 m and 1 m high. In the round chamber, which is 12 m below the entrance to the shaft, there are three stone slabs, the middle one of which contains a partial inscription of Sura 2, verse 255, from the Qur'an, the famous Ayatul Kursi, Verse of the Throne.
In 1981 Seev Jevin, the former director of the Israel Antiquities Authority, entered the passage after a group of Jewish settlers from Hebron had entered the chamber via the entrance near the mihrab and discovered the square stone in the round chamber that concealed the cave entrance. The reports state that after entering the first cave, which Jevin regarded as empty, he found a passage leading to a second oval chamber, smaller than the first, which contained shards of pottery and a wine jug.
After the Six-Day War in 1967, in which Israel gained control of Hebron, the first Jew who entered the Cave of Machpelah for about 700 years, was the Chief Rabbi of the Israel Defense Forces, Major general Rabbi Shlomo Goren. "About 700 years ago, the Muslim Mamelukes conquered Hebron, declared the structure a mosque and forbade entry to Jews, who were not allowed past the seventh step on a staircase outside the building." Following the 1929 Hebron massacre, this restricted access was even more restricted by British Mandate authorities.[citation needed] After Israeli statehood in 1948 and the Jordanian occupation of the West Bank, no Jews were allowed anywhere in the Judaean Mountains.[citation needed] Following the Israeli occupation of Hebron in the Six-Day War, the area came back under Jewish authority for the first time in 2,000 years and the 700-year-long restriction limiting Jews to the seventh step outside was lifted. Jews immediately began re-settling in the city after the Six-Day War, fixing their expulsion following the 1929 Hebron massacre. The first subsequent Jewish wedding ceremony took place on August 7, 1968.
http://en.wikipedia.org/wiki/Cave_of_the_Patriarchs
The following is an excerpt from a different website giving more insight of the 12 year old girl, Michal, going into the underground room.
Most unfortunately, the keys, and with them the responsibility, for this site was given to the Waqf, Muslim fanatics, by the then Minister of Defense, Moshe Dayan. They made every effort to prevent any permanent presence at the Caves. Among other things, they attempted to stop even Jewish worship at the site altogether. They also prevented any possibility of Jews entering the underground tombs.
Moshe Dayan, an amateur archeologist, when realizing the consequences of his action, tried to seek information concerning the underground caverns. (Perhaps he was searching for artifacts to add to his personal collection?!) In any case, any formal or official investigation was impossible. He therefore decided upon an unusual method to quench his curiosity. Within the large hall, called “the Yitzhak Hall” there is a hole in the floor, from which candles are lowered into the cave below. According to prevalent rumors, this was an entrance into the Caves of the Machpelah themselves. However, the diameter of the hole was extremely narrow - 26 centimeters. No adult could possibly fit through this opening, but Dayan found a solution. A 12 year old girl named Michal, young but courageous, agreed to be lowered into the underground room.
One misty night, Dayan ordered the Muslim guards to leave the building. He told them that they must leave for “reasons of security”. They had no idea what was about to take place. Using the dark night as a cover, Michal was brought to the site. The opening was uncovered and Michal was lowered into the underground room. The spectators were filled with suspense and worry when the girl disappeared from sight.
Michal found herself in a round room, whose floor was covered with coins, candles, and written notes. Looking around, she saw a narrow, dark corridor, to the south. The brave girl entered this hallway and after 17 meters discovered a stairwell. In total darkness she climbed the steps. After 15 steps she found a wall blocking her way. A large stone prevented her from continuing. She tried to move the stone, but to no avail. It wouldn’t budge. Having no other choice, she turned around, descended the stairs, and headed back to the small room via the narrow corridor. There, she was lifted out of the room back into the Yitzhak Hall. She was happily received, and was totally unharmed.
http://www.hebron.com/english/article.php?id=282