The Castle of Diósgyőr is a medieval castle in the historical town of Diósgyőr which is now part of the Northern Hungarian city Miskolc.

The first castle of Diósgyőr was built probably in the 12th century and was destroyed during the Mongol invasion (1241–42). The current, Gothic castle was built after the invasion and reached the peak of its importance during the reign of King Louis the Great (1342-1382). Later it became a wedding gift for the queens of Hungary, which it remained until the Ottoman invasion of Hungary in the 16th century. By the end of the 17th century it was already in ruins. Archaeological excavations started in the 1960s. In 2014 the castle was completely rebuilt, the reconstructed rooms are furnished with Mediaeval-style furniture.

The first castle was built in the 12th century, it is likely that it was an earthwork and timber castle and was destroyed during the Mongol invasion (1241–1242.) The castle that stands today was probably built by King Béla IV, who, after the Mongols left the country, ordered a castle to be built on every hilltop. In the earliest times the castle was an oval structure with a rounded donjon, surrounded by a polygonal outer wall. In 1316 it was mentioned as "new castle", which confirms the theory that it was built in place of a destroyed castle. Judging from a document listing the taxes paid by towns in 1330 it seems the town around the castle was one of the richest towns of the county.

The castle had its prime during the reign of Louis I (Louis the Great). Its importance lay in standing near the road leading to Poland (the mother of Louis the Great, Elizabeth Lokietkówna, was a Polish princess; Louis himself became King of Poland in 1370.) The king had the castle rebuilt and modernised. Surrounded by several walls, the inner castle was built around a rectangular courtyard, and it had four towers, one on each corner. On the first floor were the storerooms and on the second floor were the rooms and the Knights' Hall, which was 25 meters long and 13 meters wide. The modernising of the castle was finished under the reign of Louis' daughter Mary. The castle was surrounded by a 4 metre deep moat.

In 1364 the nearby town Miskolc was annexed to the Diósgyőr estate. In 1381 the Peace Treaty of Turin was signed in the castle of Diósgyőr. In the treaty the Italian town of Venice was compelled to raise the flag of the Anjou dynasty on the St. Mark square every Sunday. In the north-eastern tower of the castle there is a waxworks exhibition showing the wax figures of King Louis and the Venetian envoy.

Diósgyőr lost some of its importance when the personal union between Hungary and Poland ended (Louis shared the two countries between his two daughters Mary and Jadwiga.) For the next few centuries the castle was a holiday residence for queens. The last queen owning the castle was Maria, wife of Louis II. She gave up the castle formally in 1546 (by this time it had been occupied by the ruling prince of Transylvania.)

When the Ottoman army began to occupy the southern territories of Hungary, the castle was fortified. Its owners, the Gyarmati Balassa family turned it into a large fortress, and they had an Italian-style rondelle built to the north-western tower. The slim turrets were replaced by strong bastions. This was the last time the castle was rebuilt; after 1564 the owners changed frequently, and the castle slowly deteriorated. In 1596 the Ottoman army occupied the Castle of Eger and defeated the Christian army at Mezőkeresztes. The castle of Diósgyőr fell too; it was built to be a holiday residence and was never intended to be a large fortress that withstands the siege of a foreign army. From this time Diósgyőr was under Ottoman occupation and the area was ruled by the Pasha of Eger until 1687 when this part of the country was freed from Turkish rule. By this time the castle lost all of its military importance.

The restoration of the castle began in 1953. Originally only the parts threatened with collapsing were restored, the archaeological excavation began only in 1960. In the early 21st century plans to rebuild the castle were made, and by August 2014 the castle was almost completely rebuilt.

Before 2014 there was an exhibition of the history of the castle and the Pauline monastery, a weapons exhibition and the waxworks showing the signing of the Torino Peace Treaty in the northeastern tower (which belonged to the King's quarters). The north-western tower functions as a looking-tower, with a view on Diósgyőr and the surrounding hills; on the ground floor there is a small mint where tourists can make commemorative coins with their own hands. The south-western tower is in ruins. One of the main tourist attractions of the castle is a larger waxworks exhibition in the outer castle. This exhibition is one of the largest waxworks exhibitions of Central Europe and it shows six scenes of everyday life in medieval Diósgyőr.

The Castle Plays are held twice in every year (May and August). Reviving the Middle Ages, the reign of King Louis and events of Hungarian history, tournaments and open air plays are held, and there is a medieval fair next to the castle. An important musical event, the Kaláka Folk Festival is held on the second weekend of July each year.

Unlike the castles of Eger and Kőszeg, the castle of Diósgyőr is surrounded by modern concrete buildings instead of a historical town, but it is still a popular tourist destination, thanks to the castle plays, the museum, the waxworks exhibitions and Mrs. Déry's House, a small museum dedicated to the popular 19th century actress Róza Széppataki Déry, in the house where she lived.

A várban 1934–36-ban már folyt tudományos igényű feltárás. A vár helyreállítása 1953-ban indult meg, 1955 és 1961 között több méter magas feltöltést hordtak ki a várból, és ekkor még csak az életveszélyesen romos részeket hozták rendbe. 1960-tól a régészeti feltárás is megkezdődött. A rondellát Ferenczy Károly építész hozta rendbe. 1962-ben az Országos Műemléki Felügyelőség vette át a feltárás irányítását, és Czeglédy Ilona régészt bízta meg a további feltárással. A feltárt műemlék és nagy mennyiségű lelet bemutatására 1968 augusztusában alakult meg a Diósgyőri Vármúzeum. A négy torony közül az északkeletiben (a volt királyi lakosztály tornya) akkor vártörténeti kiállítás, fegyverkiállítás és a torinói békének emléket állító panoptikum volt látható Nagy Lajos király és a velencei követ viaszfiguráival; az északnyugatiban kilátó működött, földszintjén pedig éremverde (jelenleg is működik), ahol a turista saját kezűleg készíthet emlékérmet magának; a délkeleti torony (az egykori királynéi lakosztály) ép, de a turisták számára zárva van (többnyire öltözőként szolgál a Várjátékok szereplői számára); a délnyugati torony romos. A vár turisztikai látványosságaihoz hozzátartozik egy valamivel nagyobb panoptikum a külső várban, itt hat életkép nyújt betekintést a középkori Diósgyőr mindennapjaiba. A vár évente kétszer otthont nyújt a Diósgyőri várjátékoknak, mely során Nagy Lajos korát elevenítik fel, lovagi tornák és más előadások tekinthetők meg, a vár mellett pedig középkori vásár zajlik. A 2014-es felújítás előtt a vár középső udvarán szabadtéri színielőadásokat tartottak, a nézőtéren 800 ember fért el.

A vár turisztikai vonzerejéből levon valamennyit a tény, hogy a környék viszontagságos történelmének köszönhetően nem veszi körül akkora történelmi városrész, mint az egri vagy a kőszegi várat, és vadregényes erdők mellett a kevésbé romantikus diósgyőri lakótelep bérházai is környezetül szolgálnak neki. Azonban a közelben van a Bükk-vidék központi része, amely növeli a vonzerejét. Figyelemre méltó többek között a közvetlenül a vár szomszédságában álló Déryné-ház, amely a 19. század kedvelt színésznőjének szentelt múzeum, illetve a kissé távolabbi katolikus templom melletti középkori Mária-oszlop.

2014-ben a várat 2,7 milliárd forintos beruházással újjáépítették, melynek során nemcsak a romok konzerválása, hanem a továbbépítése, rekonstrukciója is megtörtént. A vár két szint magasságig újra felépült, a délnyugati torony kivételével. A délnyugati torony még jóval régebben, egy villámcsapás miatt rongálódott meg, ezért és az antik hatás kedvéért a tornyot nem állították helyre. A másik három újjászületett palotaszárnyban helyreállították Közép-Európa legnagyobb lovagtermét, a várkápolnát és a királynék lakótermét is. A felújítás eredeti tervek és korabeli festmények alapján készült.[4] A felújított várat 2014. augusztus 30-án adták át.[5]

A vár szomszédságában – részben a Várfürdő területét is elfoglalva – 2015 augusztusára készült el a Lovagi tornák tere, ahol lovas rendezvényeket, lovagi tornákat, sporteseményeket tartanak, emellett szabadtéri színházi előadások, koncertek megrendezésére is alkalmas.