"
It lies unknown
The land of mine
A hidden gate
To save us from the shadow fall
The lord of water spoke
In the silence
Words of wisdom
I've seen the end of all
Be aware the storm gets
Ulmo was the Vala who took control of the oceans in Arda hence the name "The lord of water". He had foreseen Morgoth's power eventually storming over the elves in the future despite their most valiant efforts to defeat him.
In order to save the elves from this encroaching storm, he visited the Noldor prince Turgon in a dream and guided him to the hidden valley of Tumladen which was previously an unknown land to most beings.