What's a must in the 16th?
 

Staying at the Hotel Square and could use any insider info of the area. Thanks, Theresa in Detroit

Castel Beranger and other Guimard buildings.

Great looking hotel. Bit pricey,but.

The three things I would suggest are the Trocadero, the Modern Art Museum, and the Arc de Triomphe

I would not miss Musée Marmottan.

Rue Mallet-Stevens if you have an interest in architecture.