The term Sheol in Hebrew has a number of ways in which it can be used. It oftentimes refers to the grave. Sheol can have much more of a negative connotation in terms of the wicked going to that place (Psalm 49:9, Isaiah 38:17).
Moreover, the motif of divine judgement can clearly be seen in the Old Testament. Jesus Christ Himself elaborated on the reality of hell. For example, He quoted Isaiah 66:24 in His teaching on this subject in Mark 9:47-48.
The nature of hell was something heavily speculated about by the Jews. The Jewish Encyclopedia contains the following entry:
"There are three categories of men; the wholly pious and the arch-sinners are not purified, but only those between these two classes (Ab. R. N. 41). A similar view is expressed in the Babylonian Talmud, which adds that those who have sinned themselves but have not led others into sin remain for twelve months in Gehenna; "after twelve months their bodies are destroyed, their souls are burned, and the wind strews the ashes under the feet of the pious. But as regards the heretics, etc., and Jeroboam, Nebat's son, hell shall pass away, but they shall not pass away" (R. H. 17a; comp. Shab. 33b). All that descend into Gehenna shall come up again, with the exception of three classes of men: those who have committed adultery, or shamed their neighbors, or vilified them (B. M. 58b). The felicity of the pious in paradise excites the wrath of the sinners who behold it when they come from hell (Lev. R. xxxii.). The Book of Enoch (xxvii. 3, xlviii. 9, lxii. 12) paraphrases this thought by saying that the pious rejoice in the pains of hell suffered by the sinners. Abraham takes the damned to his bosom ('Er. 19a; comp. Luke xvi. 19-31). The fire of Gehenna does not touch the Jewish sinners because they confess their sins before the gates of hell and return to God ('Er. 19a)."