Some welcome news if you’re wanting to play Cities: Skylines with Steam workshop mods in offline mode.
Steam has issued a fix in the beta client which will now let the workshop items be used without having to be online (no more copying to local folders required).
To join the Steam client beta, go to your Steam settings. In the Account section (which should be selected by default) there is a Beta participation area; click Change, and in the list select Steam Beta Update. Steam will probably require you to restart it in order to install the beta version.
Until Steam rolls this update out across its main client, you’ll need to stay opted-in to the beta version.
Once installed, if you wish to use the offline mode, toggle it like you would normally do. Launch Cities: Skylines normally and any workshop items which are already subscribed and installed should remain in the Content Manager, just as it currently does when you’re online.
If you hit the message: “Failed to Contact Key Server”, try following these steps from Steam support to get it sorted out.
Problem Occurs After Updating Steam
If this problem occurred directly after a Steam update and the firewall is already disabled, please try this process:
1. Log out and exit Steam.
2. Navigate to C:Program FilesSteam (the default location). If you have installed Steam to a different folder, please locate that folder now.
3. Rename the file “ClientRegistry.blob” to ClientRegistryOld.blob and then close the Steam folder.
4. Launch Steam and login. Steam should update, re-create the file, and then you will be able to play.