Initially the cache was hidden near the Technical University of Sofia but was later moved to a more suitable location.
To find the box you have to learn more about how Masons hide their secrets and as a true seeker of treasures you should unlock their secrets. I strongly recommend this lecture.
To find the exact coordinates you have to decrypt the following message:
For this purpose first of all you have to obtain the KEY. It can be easily obtained from the first (university's) link shown above. Take the first letters from the first and third words, the second letter from the second word and the fourth letter from the last word. Once the key is obtained you should use it to modify the order of the symbols in the Masonic pig-pen cipher. Then use the trick with Dürer's magic square (as shown in the lecture above) and hopefully you're almost ready 
Non exigo!
After decryption you will get two numbers - X and Y. The cache is at N 42° 41.(X + 123) E 023° 18.(Y + 350).
You can check the final coordinates on:
And one last thing! If you find the treasure, don't forget to keep the secret about its place, even from your own cacher friends. Only a few of the fraternity are worthy of finding The Lost Symbol!
In case the cache is missing I will appreciate if you place a temporary container until I do maintenance. Happy geocaching!