How am I able to let my 2 PC over internet see one another as if they are on the same network segment?
You can use VPN for that. It's the best solution. Also, if you need to work into your other PC like if you were seat in front of that, you can try TeamViewer.
By the other hand, like @Ron Maupin said, if you can control the routing of your organization, or enterprise, whatever, you can create a tunnel accros the internet, eg: GRE, IPsec(this one is a VPN).
You want a VPN for this.
The traditional way to do this is to configure your router as a VPN server, then have clients connect to it over the internet using some VPN software. This lets them access hosts in the LAN as if they were on the network locally.
A quick and easy alternative is to use some VPN software like hamachi or teamviewer. Both work differently, but will allow two (or more... depending on the software) computers to connect to each other as if on the same network, over the internet.
You should be able to create a tunnel from one router to the other to make your two networks look as if they are directly connected. This has the benefit of letting the routing protocols, etc, work over the tunnel.
You need to be careful if you have overlapping network addressing at both sites, but there are ways around that which involve NAT. It should only be a temporary solution to give you time to re-address one or both sides to create a common addressing scheme.