Both sentences are grammatical, but they have different meanings. To understand them, let's look at the first two definitions of the word indeed, according to the Oxford English Dictionary:
a. In actual fact, in reality, in truth; really, truly, assuredly, positively
b. Frequently placed after a word in order to emphasize it: hence, with n. = actual, real, true, genuine; with adj. or adv. = really and truly.
Your first sentence uses definition 1a. That is, "it was indeed insane" means "it really was insane." To me, this usage implies that, originally, you weren't sure it was insane (or thought it wasn't), but then learned something that confirmed that it was.
Your second sentence, I'd argue, uses definition 1b. Here, indeed is strengthening insane; "it was insane indeed" is similar to "it was really insane".
Basically, both are correct, and it's just a matter of which meaning you're going for.