Whats actually inside an ISP?

I was wondering what's actually inside an ISP. Google just said, "it connects your computer to the internet" which is just too high level for my curiosity. It is a bunch on network switches connecting all connected routers? That seems horribly inefficient.

You're assumptions are basically correct... It's mostly routers, switches, servers, and the media that connects those devices... I am a network engineer for a company that is an ISP, among other things, and if I go back in the CO (Central Office) and look at what "the Internet" is, it's basically a bunch of routers and switches and the interconnecting hardware. Facing the customer there are some electronics (DSLAMs, Calix Fiber Optic equipment, etc.), racks and racks of servers, and out of the core routers there is fiber optic cable heading off to the next network "hop" in a few different directions.

Basically, when your "internet" traffic gets to us (your ISP), we look at it and see if it needs to go to one of our servers in our data center in which case we handle that connection, or we need to pass it on down to the next node in the network based on series of dynamic routing tables that try to optimize the flow of traffic as much as possible based on the destination address of your "internet" traffic. In other words we just switch and route the traffic to the next Internet provider. Your ISP is the first real node in that network, and they may have multiple data centers of their own that it passes through or routes to as well.

I have built a number of ISP's, and@acejavelin answer is simplistic.

In the simplest terms, and ISP is really just someone that has Internet and shares this Internet with others. An ISP can be as little as a router with a WAN connection and connections to other entities.

In reality, Internet is a volume business, and contains large networks of routers and switches, but importantly also includes the support infrastructure - this is things like cooling/air conditioning, Uninterruptible power (UPS + generators), structured racks and cabling, monitoring and support systems, failover systems, fire supression systems, data storage systems and customized billing systems.