Unter den Linden Boulevard stretches from Brandenburg Gate to Schlossbrücke (palace bridge), at the heart of Berlin’s Mitte quarter. It exists since 1573, but rose to importance under Friedrich the Great. The linden trees (lime) were cut down by Hitler’s order (he had very different plans for that place). The buildings were pretty much destroyed in WW2. Some were reconstructed, others built anew. The trees were of course planted again.
Linden trees, btw, are associated with an ancient Nordic goddess named Freyja, which is considered to be the goddess of love, lust, life, fortune, truth (and all sort of things, some nice, some less). The trees are also supposed to have, if you believe in such stuff, some protective power against evil and catastrophe.
There is a lot to see on this one boulevard. For starters, when you walk from the Brandenburg Gate eastwards, you have the Russian embassy on your right (and several other embassies nearby, such as the British, the Hungarian etc, and the US embassy is planning to return there somewhen).
Walk a little further along the boulevard, and you will see on your left the famous Einstein Café, to which we’ll dedicate an entry of its own. Later on you have the Deutsche Guggenheim Berlin (Unter den Linden 13-15), Staatsbibliothek (State Library, at no. 8), Kronprinzenpalais (Unter den Linden 3), German History Museum (Unter den Linden 2) and also the Zeughaus (arsenal), the Humboldt University, Bebelplatz, Alte Bibliothek (old library), St. Hedwig cathedral and the Neue Wache memorial. And later on you get to the Berliner Dom and Museum Insel. Some of these deserve further attention (or at least we gave them further attention. I’m sure they’re all fascinating).
Also, on Unter den Linden 40 (near Einstein Café) you can find a very nice store called “Berlin Story“, in which you can find many books about Berlin, including maps and guides, and all sorts of souvenirs (not to be confused with the “Story of Berlin” museum on Ku’damm). And the boulevard is crammed with other souvenir shops, cafés and restaurants.