In the sentence "taihen tanoshii haikingu deshita," the "tanoshii" is describing the hike. The literal translation would be "a very fun hike it was," like Yoda speak, which is correct in Japanese. However, you could also say, "haikingu wa taihen tanoshikatta desu," which means almost the same thing (it may sound more like hiking in general, but it is also grammatically correct). Hope this helped! 日本語を勉強するのは頑張ってね！

Totemo omoshiroi eiga deshita. is correct Japanese. omoshiroi eiga is a noun. omoshiroi eiga deshita. translated to It was an interesting movie. i adjective dictionary form connects to noun.