Tons, no joke. It's honestly an incredibly lively city. Because it is still relatively up and coming, it's a very affordable city in regards to rent, food, drink, events, etc.
If you are an avid hiker, you probably already know that the
Northeast pales in comparison to the West, but there are still good trails around, however generally require a car to get to. I love biking and there is a really great bike trail from Philadelphia that goes all the way to Valley Forge and beyond.
To get a sense of what goes on in Philly, especially in the summer, this is a blog that my friends and I use to keep track of all the things going on in the city that seem interesting.
There's also plenty of down time in your pre-clinical years, haha.