There is a direct bus to Istanbul from Popovo.
Istanbul is a gem. Don't miss mackerel sandwiches on the docks, a stroll through the spice markets and a visit to the Museum of Innocence. A feast for the eyes and stomache with interesting tasty food at every turn. The modern art museum, the Istanbul Modern is worth a visit. Go to Galata Tower at dusk and watch the city lights come on as you listen to the muezzin, the call to prayer. The beautiful Haghia Sophia was built in the 6th century and was the largest church in the world for a long time. You can wile away hours strolling through the alleyways of Beyoglu and the other neighbourhoods surrounding Taksim Square which are full of bars and shops - a whole world of their own.
Then come to Wild Thyme for a chill.