This thesis reports on aspects of semiclassical gravity with an eye towards holography.

Chapter 2 introduces a perturbatively traversable wormhole in a particular four-dimensional quotient spacetime, where traversability is ensured by the Casimir energy of bulk fermions. We compute the fermionic contribution to the integrated null stress-energy tensor and find hints that traversability holds at all times.

Chapters 3 and 4 report on computations of entanglement negativity, a multipartite entanglement measure which distinguishes between classical and quantum correlations. We compute holographic entanglement negativity in a toy model of Jackiw-Teitelboim gravity with end-of-the-world branes, finding a rich phase structure which includes replica symmetry breaking in a large region of phase space. We also compute entanglement negativity in a toy model of chaotic eigenstates, finding some qualitative agreement with phase transitions in the holographic model.

Chapter 5 describes a modification to random tensor networks to incorporate bulk gauge symmetries which we term the "gauged random tensor network." We find an area operator valued in the center of the gauged random tensor network bulk algebra which more closely resembles the area operator provided by the quantum-corrected Ryu-Takayanagi formula.