The Fourth Riddle

Here's one that I wrote myself. It's not very good, but here goes:

I am a box with not much to show
Only liquid and trees within me are known
You turn my lid and open me up
Explore new worlds with me on up
To places where not many can go
Like mountains high and valleys low
Oceans deep and rivers long
Hey, I might even contain a song
So open me up and dive right in
Then close me up and start again

What am I?