After just recently visiting Scotland, I am a bit disappointed I did not manage to get to visit this famous place.The Chapel, also known as St. Matthew's Collegiate Church is a working church.
It has been brought to public attention once more with the Dan Brown book, "The Da Vinci code", and was a location in the film.
Rosslyn Chapel lies approximately five miles (8km) south of Edinburgh. It was built on the orders of Sir William St Clair, the third and last Prince of Orkney, between 1440 and 1490, to be a private place of worship for his family.
Many theories abound about what could be hidden within the chapel,including:
The lost gospels of Christ are secreted somewhere within the chapel, taken there by the Knights Templars.
The Holy Grail lies hidden beneath the building.
The Ark of the Covenant is there.
And even the mummified head of Christ (or alternatively John the Baptist) is hidden there.
and so it goes....
It could be that there is no actual physical treasure there, but a spiritual/mystical truth that has been entrusted to this ancient building.
In the building of the chapel, The best stone masons of Europe were brought in to work the stones. There is much symbolism and geometry carved into the stonework, which is very well preserved.
To add to the Templar connection - Sir William St Clair was a member of the Knights Templar order and it was him who personally over saw all work and decorations to the building.
The name Rosslyn in itself has been said to have different meanings:
Rosslyn is a form of the phrase "Rose line", and that a line starting in France also runs through the Chapel
"Rosslyn" comes from two words "Ross," meaning steep cliff, and "Lyn", meaning fast-flowing water
'Ros' and 'Lyn' which have their roots in the Gaelic:'Ros', meaning ancient knowledge and 'Lyn', meaning down the ages.
Could it be then, that important knowledge has been encoded into the stonework, only accessible if one knows the code?
There is also thought to be a ghost in residence, one stone mason apprentice who was killed by his master, because he finished work on a pillar that his master was working on(nice times).
The mystery still lingers regarding Rosslyn chapel.
You can visit the chapel website and view the carvings at:
http://www.rosslynchapel.org.uk/
I had a look at various photos of it -- amazingly ornate! 
