What’s the name of the park. That’s one place to visit just from the pictures alone...
It's called Bois de Vincennes (The woods of Vincennes). It's the largest park in Paris.
To give an idea of size is about three times larger than Central Park in New York.
If you've been to Paris before this might be a place to check out on your second or third trip. It's a bit out of the way from the main sites and other interesting bits.
Chateau de Vincennes is nice as well as the suburb/town of Vincennes.
The structure in the picture is called Temple d'Amour or Temple of Love. It sits on an island of one of the four lakes in the park and there's a Buddhist temple nearby
Bois de Vincennes is also the end/beginning of Promenade Plantée, sort of.
Most people when they visit Paris for the first time they stick to the 1-7 arrondissements because that's where everything touristy is.