There's more things under hydra, but it looks like this: /nix/var/nix/gcroots/hydra/ik699gs9w3s6l3gii4p0fbcw2a2r6mh2-blog-content.drv
/nix/var/nix/gcroots/hydra/jl9gd1ia53zwhqh3h762lvifnrk8664p-blog-generator-0.1.0.0
/nix/var/nix/gcroots/hydra/lqqf4fqyra2zskv2siv3nrr1wpblcyan-blog-generator-0.1.0.0
/nix/var/nix/gcroots/hydra/lx3n8xwyvi9lcx1vvv7n583h8yd8m5gc-blog-content
/nix/var/nix/profiles/blog-34-link