I spent the day in Istanbul mainly eating, sipping Turkish coffee and wandering around. It was delightful. I finally figured out how to get the Istanbul Metro Card which works on all of the different trams and subways. That made getting around much, much easier.
I found more and more charming little areas and markets for the locals with hundreds of restaurants and cafes. I was going to go into the Basilica Cistern but they only accepted cash and I didn't want to get anymore Turkish Lira.
When I checked out of the hotel in the morning, they let me leave my big bag in storage. I picked it up and 18:00 and went to the Esenler Coach Terminal where the overnight bus to Sofia, Bulgaria departs. The Otogar Metro Station is right in the middle of the bus terminal. There is also a little shopping area lined with restaurants inside the huge, hollow, square bus terminal. The bus terminal is technically in Bayrampaşa and that's what is said on my bus ticket.
At the bus station, I went to an internet cafe and watched YouTube videos to kill time until my bus left at 21:00. The bus had a great seat configuration with a single seat on one side of the aisle and two seats on the other side. Of course, I took the first single seat. Not having anyone next to you is a luxury.
The bus ride was pretty easy and I was able to sleep quite a bit. The bus stopped every couple of hours to get gas and let us use the toilet. The border crossing to Bulgaria was also easy even though we had to get off the bus and go through immigration. There were only about 15 people on our bus. Since I was sitting in the front I was almost first in line for the exit from Turkey and entrance to Bulgaria.