"Don't Do Sadness/Blue Wind" from SPRING AWAKENING (lyrics in "Blue Wind" include summer). It's a male solo song and female solo song that interlaces.
"Song of Purple Summer" from SPRING AWAKENING, but it is a choral number which I guess could be a duet.
"The Colors of Paradise" from THE SPITFIRE GRILL (female duet, although more of a Spring song).
"Our Last Summer" from MAMMA MIA!
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle