I need to build a Python application that receives highly secure data, decrypts it, and processes & stores in a database. My server may be anywhere in the world so direct connection is not feasible. What is the safest/smartest way to securely transmit data from one server to another (think government/bank-level security). I know this is quite vague but part of the reason for that is to not limit the scope of answers received.
Basically, if you were building an app between two banks (this has nothing to do with banks but just for reference), how would you securely transmit the data? 
Sorry, I should also add SFTP probably will not cut it since this python app must fire when it is pinged from the other server with a secure data transmission.
What is the safest/smartest way to securely transmit data from one server to another (think government/bank-level security)

It depends on your threat model, but intrasite VPN is sometimes used to tunnel traffic like this.
If you want to move up in the protocol stack, then mutual authentication with the client pinning the server's public key would be a good option.
In contrast, I used to perform security architecture work for a US investment bank. They did not use anything - they felt the leased line between data centers provided enough security.
Most secure server to server connection