Ahlden House Ahlden House ( ) is a stately home at Ahlden on the Lüneburg Heath in Lower Saxony , Germany . It was built in 1549 as a water castle on the river Aller , which has since changed its course . Nowadays the three - winged mansion is a private residence and is used as an arts auction house . It is principally known as the place of imprisonment of Sophia Dorothea of Celle , otherwise Sophie Dorothea of Brunswick - Lüneburg , wife of George I of Great Britain and the mother of George II of Great Britain . Location . Opposite the mansion , in a depression on the other bank of the river , was the old castle of Bunkenburg which lies today in ruins . It is believed to have been built in the 13th century . It was established opposite the village of Ahlden on the banks of the Aller . In 1618 , during a flood , the Aller shifted its channel towards the east and , as the result of an embankment downstream , the waters of the Leine then flowed past Ahlden in the bed of the former Aller . Since 1648 the course of the " Old Leine " has become a partly dried oxbow lake . The present house was built in the 16th century on the river bank by Ahlden opposite the Bunkenburg . Today it is located on the old branch of the Aller , which was the one that channeled the waters of the Leine in 1618 and has since been called the " Old Leine " . Construction . Much of the house is of timber - framed construction ; only the ground floor of the west wing being built of brick . The building today consists of three , two - storey wings in the shape of a horseshoe , which were built in 1549 . In earlier centuries the site was , for a time , almost entirely enclosed and had an interior courtyard . The individual wings of the building were not only used for residential rooms , but as for stable s and coach house s ( " Remisen " ) . The west wing is the main building of the mansion , which Duke Christian the Elder of Brunswick - Lüneburg had built by his seneschal ( " Drost " ) , Johann Behr , in 1613 . On the entranceway leading to the inner courtyard the wall recesses for the drawbridge can still be seen . During the construction of the wing in 1613 there was a serious accident when a roof joist dislodged and seriously injured 14 workers . The south wing , a timber - framed structure with brick infill , is the oldest part of the building . It was completed in 1579 under Duke William the Younger of Brunswick - Lüneburg , as an inscription on one of the beams records . The inner courtyard side of the wing has a lavishly - decorated Renaissance facade . The north wing is a timber - framed structure that was redesigned in 1705 by the architect , Johann Caspar Borchmann , because the building was falling into disrepair . Outside the house there was a gatehouse and entranceway . It guarded access to the house and was demolished probably around 1800 . The building is clearly recognisable on the Merian engraving of 1654 as a detached building . Originally the castle was surrounded by a double moat and a rampart . The rampart was levelled in 1690 in order to create a French pleasure garden . The moats were filled in during the 19th century . History . The castle ' s predecessor , Bunkenburg , appeared on the opposite bank of the Aller , a detail also mentioned by Merian . The occupants of this castle were the House of Ahlden , first mentioned in the 13th century , who were knights ( " Ritter " ) and Burgmann s . The fortification was first mentioned in the records in 1433 , and had previously belonged to the Diocese of Minden . In 1431 there was a change of seat from Ahlden and its castle . The lords of Ahlden lost everything in the conflict with the diocese and the House of Welf . They had broken their bond not to pursue any more feud s or carry out any more raids . As a result Ahlden ended up in the possession of the Duke of Lüneburg . Between 1443 and 1575 the seat of Ahlden was mortgaged to the von Mandelsloh family . Not until the 16th century was the present castle built , whilst Bunkenburg fell into ruin . The princely office ( " Amt " ) of Ahlden was established in 1431 . It took over the management and exercised jurisdiction over the area . The castle also belonged to the " Amt " . The office was headed by an " Amtmann " , who collected taxes from the citizens and farmed the land on the state - owned farm , the estate of the castle . From 1784 the castle underwent major alterations to adapt it to administrative purposes and it also housed the prison . After about 450 years in existence , the " Amt " of Ahlden was disbanded in 1884 and its function was transferred to the district of Fallingbostel . The castle then housed the district court ( " Amtsgericht " ) until 1972 . Justice had been dispensed in Ahlden since 1310 . In the Thirty Years War the castle was occupied by the imperial troops under Tilly after a day ' s siege . They defended it against an unsuccessful attack by 800 besieging Danish troops . From 1726 Ahlden House was the residence of the state seneschals . The considerable renovation work required was completed in 1975 at a cost of 90 , 000 DM from state funds . An antiques auctions house bought the castle for its representational headquarters , on the condition that the castle courtyard would be kept open for the public during the day . Limited viewing of the interior is only possible when previewing items for auctions . Prison . When she was divorced from her husband in 1694 after her affair with Lieutenant Königsmarck , Sophie Dorothea of Brunswick - Lüneburg was brought to Ahlden House , where she was imprisoned until her death in 1727 .