tomb

hauta A small building (or "vault") for the remains of the dead, with walls, a roof, and (if it is to be used for more than one corpse) a door. It may be partly or wholly in the ground (except for its entrance) in a cemetery, or it may be inside a church proper or in its crypt. Single tombs may be permanently sealed; those for families (or other groups) have doors for access whenever needed.
A pit in which the dead body of a human being is deposited; a grave.
Shakespeare

As one dead in the bottom of a tomb.

I never told anyone about it. You're the first, except Ivan, of course—Ivan knows everything. He knew about it long before you. But Ivan's a tomb.