Question: "Where did Old Testament believers/saints go when they died?"
Answer: The Old Testament believers went to a place of comfort and rest called “paradise” when they died. The Old Testament taught life after death and that everyone who departed from this life went to a place of conscious existence. The general term for this place was Sheol, which could be translated “the grave” or “the realm of the dead.” The wicked were there (Psalm 9:17; 31:17; 49:14; Isaiah 5:14), and so were the righteous (Genesis 37:35; Job 14:13; Psalm 6:5; 16:10; 88:3; Isaiah 38:10).
The New Testament equivalent of Sheol is Hades. Luke 16:19–31 shows that, prior to Christ’s resurrection, Hades was divided into two realms: a place of comfort where Lazarus was (Abraham’s bosom or Abraham’s side) and a place of torment where the rich man was (hell). Lazarus’s place of comfort is elsewhere called “paradise” (Luke 23:43). The place of torment is called “Gehenna” in the Greek in Mark 9:45. Between paradise and hell (the two districts of Hades) there was “a great chasm” (Luke 16:26). The fact that no one could cross this chasm indicates that, after death, one’s fate is sealed.
Today, when an unbeliever dies, he follows the Old Testament unbelievers to the torment side of Hades. At the final judgment, Hades will be emptied before the Great White Throne, where its occupants will be judged prior to entering the lake of fire (Revelation 20:13–15).
On the other hand, when a believer dies today, he is “present with the Lord” in heaven (2 Corinthians 5:6–9). There, he joins the Old Testament saints who have been enjoying their reward for thousands of years.