Kodesh HaKodashim (Holy of Holies)
The Kodesh HaKodashim is the holiest spot in the entire Beit HaMikdash thus being the holiest point in the world. It is only entered on Yom Kippur (the Day of Atonement) by the Kohen Gadol (High Priest) and is separated from the Kodesh (Holy) by a curtain called the Parochet.
The Kodesh HaKodashim through the ages:
Mishkan (Tabernacle)-The Kodesh HaKodashim was 10x10x10 amot (handbreadths). Inside was the Aron HaBrit (Ark of the Covenant) covered with the Kaporet (cover) and the Keruvim (cherubs). Alongside the Aron was a container of Man (manna), the staff of Aharon, and a jar of the Shemen HaMishcha (anointing oil).
Bayit Rishon (First Temple)-The Kodesh HaKodashim was 20x20x20 amot. The Aron HaBrit rested on the Even HaShtiya (foundation stone). Next to it, stood the same things that were found in the Mishkan as well as a chest from the Plishtim (Philistines). King Shlomo (Solomon) also added two enormous keruvim (10 amot high) that stood side by side in the Kodesh HaKodashim.
Bayit Sheni (Second Temple)-The Kodesh HaKodashim was 20x20x40 amot. The only thing found inside during Bayit Sheni was the Even HaShtiya.