Where and how do pip installs of Pytorch install CUDA

When you install Pytorch via pip, I’m aware that it downloads a precompiled CUDA runtime that works with that version of Torch.

However, I cannot seem to find any information on how this works, or where the downloaded runtimes are placed. In a related issue, my version of Torch was clearly built with CUDA, yet doesn’t seem to be able to find any cuda runtimes - how is this possible?

Collecting environment information...
PyTorch version: 1.5.1
Is debug build: No
CUDA used to build PyTorch: 10.2

OS: Ubuntu 16.04.6 LTS
GCC version: Could not collect
CMake version: Could not collect

Python version: 3.6
Is CUDA available: No
CUDA runtime version: No CUDA
GPU models and configuration: No CUDA
Nvidia driver version: No CUDA
cuDNN version: No CUDA

Versions of relevant libraries:
[pip3] numpy==1.19.0
[pip3] torch==1.5.1
[pip3] torchvision==0.2.0

Any information on how pip + pytorch manage the cuda runtime installation, and where this runtime is stored, would be helpful.