Goa... if you haven't been there yet... and if you have already, visit once more and this time not just the beaches.
The weather would be nice, the touristy season is yet to begin in December... so it will be less crowded, less expensive and more fun!
"Hello! It depends on what do you want to do. If you're going to have fun, visit cool clubs, bars, and just relax, then you can go to Berlin or Amsterdam. Those two cities are the best to hang out with friends and have an unforgettable time. But if you want to explore cities, visit museums, have different excursions, then I can recommend you to visit Russia. I was there two months ago, and it was something new to me. I've been to Moscow and St. Petersburg, and the second town stole my heart. The architecture is beautiful, there are so many historical museums, Hermitage, for example, is the must-visit place. I've spent two days in Moscow; then I bought a train ticket at https://www.russiantrain.com (the train was called Sapsan, fast and comfortable one) and in a few hours I came to St. Petersburg, where I also stayed for two days. It's enough to explore the most exciting places, and if you will decide to go there, there is no need to stay longer.
I hope you'll have a great trip!"