How to auto mount / permanently mount external devices on NixOS

I have a USB stick and an NTFS hard drive partition that I'd want to use in NixOS. On some other distribution, I'd mount it using ntfs-3g in /mnt. But on NixOS, the directory doesn't exist; I suppose NixOS has some other canonical way and/or place of doing that. In NixOS, how should one set up automounting of external partitions, preferably using configuration.nix?