You may stay for a week in Lviv and no resident would mention this sad place. Though if you ask specifically about THE CITADEL everyone will point you in the right direction.
In 1848 the Polish popuation of Lviv raised a riot against the Austrian-Hungarian government. Imperial troops suppressed the national movement and Lviv suffered heavy artillery fire. Habsburgs took this lesson very seriously and decided to built a fortress at a place from where the city could be easily controlled by the artillery. So The Citadel was erected.
The complex consisted of the central building strengthened with two square towers and four round towers at the perimeter, all at the top of the hill right by the downtown Lviv. It is known that the Citadel has been used in the war of 1918-1919 between Polish and Ukranian armies. The red brick walls are speckled with marks from the shells of that period.
During most of its life the Citadel served as military barracks of different armies: Austrian, Russian, Polish and Soviet.
The WW2 became the darkest period in the history of the Citadel. Here in July 1941 the Nazis organized a so-called "Stalag-328". Being first a concentration camp Stalag-328 soon turned into a death zone for those unfortunate people who found themselves in the Citadel. Nazis kept here prisoners of war - mostly from the Red Army but also from France, Belgium and some other countries. Living conditions were much like continuous tortures. People were fed with wastes, they slept outdoor and were forced to work hard. It is known that Nazis took no care about medical treatment so many people died from various diseases. Life here was so insufferable that there were facts of cannibalism among prisoners. It is acknowledged by historians that more than 140,000 people were tortured to death and shooted in "Stalag-328" during the WW2. Their bodies were usually not buried but burned.
Today the Citadel is neither a monument nor a museum. The central building is occupied by some bank and there are numerous offices and storehouses at the top of the hill. The biggest round tower (the northern one) became a book depository and was closed for public. The second tower (the eastern one) was reconstructed. A roof ("in Chinese style" as many observers say) was added and one of the "Stalag-328" death barracks was turned into a luxury inn. Of two other round towers at the Southern border one was repaired but closed and fenced. The last one (the smallest tower of the Citadel) being ruined by a bomb was abandoned and you can get inside - though be careful since bricks used to fall from the dilapidated roof. There's no any fee to enter the territory of the Citadel and walk around.
Many people with whom I talked about the Citadel were disappointed (some of them rather angry) with its destiny, especially with a resort built at this tragic place. This may be one of reasons for Lviv inhabitants not to speak a lot about the Citadel when asked about tourist attractions of their city. Anyway, there's a huge wooden cross not far from the entrance to the northern tower and I witnessed a church divine by it which was devoted to all those who ended their lives here at the Citadel.
The complex may be approached from different points but I would recommend going up the Grabovsky Street. The attached waypoint was formerly a parking lot; in 2013 after reconstruction there is still place for parking but the road is driveable further and closer to the cache location. I leave the waypoint for better orienteering.