Hello, Kevin.
I'm glad to get your answer. It's great that you want to visit Russia with your sister. I can tell you some interesting things about different places.
So if you are interested in history and beautiful architecture you should go to Saint-Petersburg. It's the very big city. There are a lot of amazing buildings ,monuments and historical things. Also you can go to the Hermitage or Russian museum If you are a fan of pictures and sculpture. But you must be ready for rainy and windy wheater.
Have you ever heard something about Kavkaz? There is awesome nature. Kavkaz has a lot of mountains. It's the great place for skiing. So you can get much extreme feelings.

But if you want to relax and enjoy sunbath you should visit Sochi. There are many tourists in Sochi. Do you like sport? It was the city of winter Olympic games in 2014.