That's a super-nice medal. Iran. Valuable, too. The one in our picture comes from Westfälische Auktionsgesellschaft where is sold for $984 US dollars during a 2016 auction. Yours is worth about that. Here is the auction description:
Nasir al-Din Shah (AH 1264-1313) 1848-1896. Bronze medal 1873, from Wyon. On his visit to London. Half-length portrait of the Shah in uniform / The personified London, in the right scroll with 20TH / JUNE / 1873, on the sides the escutcheons of Persia and London, in the background left St. Pauls, on the right the Tower. Bucket 1623, Brown 2951. 76.4 mm.
Nasir ad-Din Shah traveled to Europe three times and visited most of the continent's capitals. The first trip in 1873 took him from Russia via Germany, England, France, Switzerland and Italy to Austria for the Vienna World's Fair. Persia was represented there with its own exhibition building, the Persian House. On his second trip to Europe, which also took him to Russia, Naser ad-Din Shah took off a parade of Russian Cossacks. He was so impressed that he asked the Czar to help build a similar force in Iran. In 1879, a military agreement was signed between Persia and Russia aimed at establishing a Persian Cossack brigade of Iranian troops and Russian officers. Czarist Russia pursued with the Cossack Brigade both economic and political interests and financed the pay of the Persian Cossack Brigade temporarily from their own resources. The Persian Cossacks were later increased to divisional strength and remained until 1920 under the command of a Russian officer. Nasir al-Din Shah was a Knight of the Order of St. Andrew the First-Called, as well as bearer of the White Eagle Order, the St. Alexander Newsky Order, the Order of St. Stanislaw and the Order of St. Anne with diamonds.
Estimate: 400 EUR