Keys to the X

What is this set of keys I found?

Theirs an insignia of an X on one

Included with these keys is a map

There is a trail and a number of landmarks on this map

Which I compare to world maps, old & new

After researching far and wide

My adventure takes me to the first location 

Where the X mark is shrouded

I uncover what is hidden underneath this X

And find an unusual box with the same X insignia

What will I find in this X marked box?

Something common or something rare?

Will it be useful, valuable, or just the next key marked X?

The adventure continues…