What a wonderful choice to have! I’ve visited both Williamstown and Philadelphia and love each for different reasons. My kid was recruited by Williams but ultimately chose to attend Penn as a non-athlete. Williamstown is beautiful but lacking in cultural amenities compared to Philly. Philly is a vibrant, diverse city where one can find something different to do each day. I would think participating in the Penn Relays on your home track would be very special.
I understand what you mean about Penn being isolated. The “Penn Bubble” exists and it’s nice because it insulates students from the city but at any point you can experience all the city has to offer. Although campus is urban, it’s not really open to West Philly; Penn police and campus security insure that.
If you’re interested in research, then you can get involved as early as your first semester. Opportunities are plentiful and available through CURF (Center for Undergraduate Research and Fellowships) and PURM (Penn Undergraduate Research Mentoring Program).
I think you have a preference though and believe you should follow your heart on this one. You say that you’re a nature lover. Really consider whether you can thrive without easy access to nature. After two years in Philly, my outdoorsy kid is already looking to greener, rural pastures for grad school. The constant hum of a city can be maddening if you prefer tranquility. Best of luck to you.