Here are compilation of the 3 riddles you receive in the 'Hidden Messages' quest in case you accidentally delete the message from your inbox.
Riddle One:
Operator,
Unfortunately the nature of the Orokin Artifact you just crafted is a mystery to me. I simply cannot fathom its use. All I can tell you was that it was inscribed with the following nonsense:
Three parts, three acts, three riddles for thee –
to revive the one wielding fantasy
Ancient gods so cruel, once ruled from on high
Can you name their peak where the land meets the sky?
Nothing in my database that sheds light on its meaning. You'd think the Orokin would have something better to do than scribble nursery rhymes on things. Oh well, I suppose not everything you craft can be of use.
Ordis, Ship's Cephalon
Riddle Two:
Operator,
To think, Ordis thought that mess of words was nothing but the scrawling of some long dead hack. You saw more. Now you have the helmet for a whole new class of Warframe. Very impressive Operator.
Exciting news. Ordis found more writing on the inside of Mirage's helmet:
To build the one you think witty,
seek the nymph who sang oh so pretty.
She lured him in with her song and grin,
his wife must've thought it a pity.
I have no idea what that means, though if I had to describe its literary merit I might use another word that rhymes with 'witty'.
Ordis, Ship's Cephalon
Riddle Three:
Operator,
It is as if the person writing these messages wanted Mirage to be found. Within the newly crafted Mirage Systems, Ordis found this:
One more act before your prize is caught.
An ancient sea creature, take a whirl or not?
Look for the monster that swallowed sailors of yore.
Make a mistake and you're sunk. Nothing more.
That's the worst one yet! Though, Ordis must admit, they are clearly referencing something. Operator, you appear to be good at this sort of thing, can you find the final blueprint?
Ordis, Ship's Cephalon