You would better choose to stay at a hotel in the city center where the transportation is more convenient. And train station is around 10km from the city centre. You can visit the nearby cities like Hangzhou, Suzhou, Shanghai and etc. since high-speed trains are operating between these cities. For the transportation and attractions in Nanjing, you can check the details on the page: https://www.travelchinaguide.com/cityguides/nanjing.htm