Was Jesus really buried in a tomb?

Yes. Before there can be an empty tomb, there has to be a tomb - so the burial is the foundation of the whole resurrection case. And it is, in the judgment of a broad range of critical historians, one of the best-established facts about Jesus. The earliest witness is not a Gospel but the pre-Pauline creed Paul quotes in 1 Corinthians 15:3-5 - "he was buried" is one of its four load-bearing clauses, and most scholars date the creed to within a few years of the crucifixion. All four Gospels then name Joseph of Arimathea, with John showing little dependence on the others.

The most powerful point is who does the burying. Joseph is "a respected member of the council" - the very Sanhedrin the Gospels blame for handing Jesus over. Inventing a pious member of the condemning body cuts directly against the early church's polemic; the Catholic scholar Raymond Brown, no apologist, called such a fiction almost inexplicable. This is the criterion of embarrassment at full strength, reinforced by the women named as witnesses to the tomb in a culture that discounted their testimony.

The strongest objection, from John Dominic Crossan, is that Rome left crucifixion victims for the dogs. That was often true across the empire - but not in Jerusalem, where Jewish law demanded same-day burial (Deuteronomy 21:22-23), Roman governors had reason to accommodate it at Passover, and a 1968 excavation found the heel bone of a crucified man, Yehohanan, given a proper burial with the nail still in it. Even the scholar Byron McCane, who argues the burial was dishonorable, concedes it was real. A known tomb is all the empty-tomb argument needs.