Epica is a Dutch symphonic metal band, founded by guitarist and vocalist Mark Jansen after his departure from After Forever. Born as a symphonic metal band with gothic tendencies, later Epica have incorporated into their sound strong death metal influences. Starting from the third album, even progressive metal attitudes have become evident. In addition, the band often uses thrash metal and groove metal riffs, black metal passages (mostly in the drum technique), power metal moments and references to Arabic music.

In an interview in November 2010, Simone stated that the band was going to start writing music around February 2011 after their Latin American tour is over. She also stated that they were hoping for a release in the first quarter of 2012. 14 tracks were written without lyrics by May 2011. The band entered the studio later that year, with Sascha Paeth once again as the producer. On December 1, the band announced that the name of the album would be Requiem for the Indifferent, and would be inspired by such factors as the enormous tension between different religions and cultures, wars, natural disasters and the financial crisis. The album was released on March 9, 2012 in Europe, and on March 13, 2012 in the United States. On March 25, 2012, Epica announced on their website that original bassist Yves Huts and Epica had parted ways, to be replaced by Rob van der Loo (ex-Delain, MaYaN). On April 24, the music video of Storm the Sorrow was officially released, earning 128,000 views on YouTube on the release day. General response to Requiem for the Indifferent was positive. Allmusic stated that the album "is a typically elaborate and ambitious affair, incorporating copious amounts of choral work and classical arrangements into the band's neatly established blend of goth, progressive, power, and symphonic metal." Natalie Zed of About.com staff considered Requiem for the Indifferent "a transitional album for the band", which tries to expand their musical range experimenting with "weird" riffing and new combination of vocals, while "losing none of the richness that has gained them fans." On 16 September 2012, the band made a guest appearance on the Dutch TV show Niks te gek (translation: "Nothing [is] too crazy"), where mentally disabled people (18 years or older) can get their wishes granted. In the episode, they recorded, together with the mildly autistic Ruurd Woltring, one of his own compositions, "Forevermore". The single was released through Nuclear Blast on 25 September 2012. The band announced on their official website that on March 23, 2013, they would celebrate the 10th anniversary of Epica in Eindhoven, Netherlands. The concert which would be called Retrospect, would be held in Klokgebouw with a 70-piece orchestra, choirs, international guests and many special effects. The band invited the Hungarian Remenyi Ede Chamber Orchestra and the Choir of Miskolc National Theatre to this show as they were the same orchestra that accompanied Epica in the recording of the live album The Classical Conspiracy. The concert consisted of a 70-piece orchestra, special effects, acrobats, guest vocalist Floor Jansen and former band members Ad Sluijter, Yves Huts and Jeroen Simons. Finnish singer Tarja Turunen was also invited to the show, but had to decline due to scheduling problems. In the show the band introduced a new song titled "Retrospect" and played "Twin Flames" from Requiem for the Indifferent for the first time. They also played for the second time their longest song "The Divine Conspiracy", however a shorter version of this song was played. During the concert, Coen Janssen announced that Retrospect would be filmed for release as a DVD. CANNOTANSWER

Answer the following question by taking a quote from the article: how did they celebrate?

The concert which would be called Retrospect, would be held in Klokgebouw with a 70-piece orchestra, choirs,