(So we did that random word thing again. This week it was mailbox.)

Walking on packed sand
Alongside morning's tide
I spy some litter on the land
And, intending to throw it out,
Instead I find a bottle peeking out
Delivered over in night’s hand
I roll the bottle in my palms
Brushing off crusted shell and sand
To find a parchment crumpled
Confined within brown glass
A moment passes as I ponder this
Mysterious and romantic cache
A lovers letter? A cry for help?
Someone far away reaching out?
A treasure map, marked with X?
The answer to the riddle