The coupling of two remote networks is known as a LAN-LAN coupling. With such a connection, the devices in one LAN can access those of the remote LAN (assuming they have the necessary access rights).
In practice, LAN-LAN couplings are frequently used between company headquarters and subsidiaries, or for connections to partner companies.
A VPN-enabled router (VPN gateway) is located at either end of the tunnel. The configuration of both VPN gateways must be matched to one another.
The connections are transparent for the remaining devices in the local networks, i. e., they appear to have a direct connection. Only the two gateways must be configured for the VPN connection.