The Secret of Monrepos

After the death of King Friedrich in 1816, Queen Charlotte Mathilde received Monrepos Palace as a widow's pension. Part of the heritage was also the famous light blue diamond that was named "Charlotte's Soul". She had the diamond set in her gold headband. On October 5, 1828, Charlotte died in Ludwigsburg. She was buried in the crypt of Ludwigsburg Palace and also wore her headband when she was laid out - but the valuable diamond had broken out and disappeared. King Wilhelm I ordered an investigation and finally a housemaid testified that Charlotte herself commissioned it shortly before her death. But the diamond remained missing despite a large-scale search. After almost 200 years, the riddle of "Charlotte's soul" is still not solved. All we know is that the diamond must still be on the castle grounds. But now there is a first clue. You found some letters from Charlotte to her relatives in London and a diary in the Ludwigsburg city archive. One of Charlotte's letters to Queen Victoria contains a clue to the whereabouts of the diamond. But Charlotte was unable to send the letter, which is dated on the anniversary of her death. Some old plans of the site were also enclosed with the letter, but unfortunately a lot has changed after 200 years, buildings were demolished, new ones were built and the park was redesigned. So it won't be easy to follow the traces that are almost 200 years old. A wiki entry gives you a few clues, but nothing more. Now you have the unique opportunity to solve the mystery of "Charlotte's soul". But your search in the archive did not go unnoticed. The archivist has been watching you and is on your heels to get the diamond as well. You're only two hours ahead...