Toledo is a very quick train ride from Madrid and it's an incredible place if you enjoy heritage and religious architecture or shopping (imo the shops are mostly tourist traps but are fun to look at). There's a 10 euro bracelet that allows you entry into I think 7 palaces, churches, etc. which is cheaper than buying entry at each place separately :)

Also not nature related but please go to Tacos El Pastor in Madrid and literally eat 20 tacos in one sitting (most tacos are 1 euro each!!!!)

If you want more Madrid recommendations DM me, I went back in May!

From Madrid, hit up Salamanca, Avila, Segovia, and Toledo. All smaller cities and a much smaller representation of Spain. Salamanca doesn’t get many tourists so they don’t speak much English but definitely worth the bus/train ride over. If you go to Valencia, check out Albufera. And the north coast between Bilbao and San Sebastián are amazing coast lines. Some game of thrones stuff was filmed there. As well as Galicia is very unique. Northern Spain is known as “green Spain”. Check out the UNESCO list too! You might get some inspiration. There are some national parks in Spain too, one near Cadiz in the south

From Athens I would suggest going to Nafplio and Delphi (the navel of the world). If you like hiking Delphi is also a very good destination, as it's very close to Mount Parnassus. You can also take the ferry to Aegina and Hydra islands

If you like wilderness and epic photos, def check out Meteora while in Greece. It has rock formations like I've never seen before. I recommend going on a walk through the woods during sunset. A bit spooky when it gets dark but super amazing. Bring a headlamp or flashlight.