Is it even possible to solo-play a two-player CDG where bluffing and hidden information makes up a big part of the gameplay, you might ask?
No- and yes!
I got 13 Days last week and have been thinking alot about the different mechanics, the DEFCON death dance and what is the most important aspect of the game to be good at.
Here's my suggestion for a very easy solo variant that obviously misses out on the bluffing aspect, but instead lets you practise board positions, risk assessment and Strategy card synergy:
You simply follow the rules like normal, taking turns playing US and USSR, with one exception: after having flagged the different Agenda alternatives for each round, you randomly select an Agenda (face-down) for each side and slide it under the board. At the end of each round, you reveal and resolve them just like normal.
This was actually more fun than it may sound, because you are forced to try to cover all alternatives as best you can, with the full tension of the two-player game. (In a way it's even more tense, as now you have only yourself to blame for nuking yourself to oblivion
The variant should work both if you just want to fool around, but also if you want to raise your understanding of the game. Good luck