The process you're describing is called subduction. It happens at subduction zones, which are areas where oceanic crust collides with continental crust.

Here's a breakdown:

* Oceanic crust is denser than continental crust.

* When these two types of crust collide, the denser oceanic crust is forced to bend and slide beneath the continental crust.

* This sinking process is called subduction, and it occurs along a subduction zone.

* As the oceanic crust sinks deeper into the mantle, it melts, generating magma that can rise to the surface and form volcanoes.

So, the answer to your question is: Oceanic crust sinks toward the mantle beneath continental crust at subduction zones.