Guru Nanak the founder of the Sikh faith lived from 1469-1539. Most of the time of his life he spent in the Punjab (the area now under control of Pakistan). From 1498 onwards the Guru started his travels which continued for about 15 years. During this time it is recorded that he visited Mecca and Baghdad and also travelled East to Dacca and South to Rameshwaram. These travels puts Nanak in the bracket of the great travelers of that era , on par with Marco Polo and Ibn Battuta.
The most talked about visit of Nanak is to Mecca. Many Muslims claim he went there for Haj as only Muslims are allowed to enter Mecca and worship at the Kaaba. Nanak also is referred to in Islam as Hazrat Rab Majid Baba Nanak Faqir. Nanak did go to Mecca, but in all likelihood as he traveled with a caravan with a choga as worn by ascetics of that age, he passed off as a Faqir. That enabled him to gain entry into Mecca, but there is no record that he offered prayers at the Kaaba.
Nanak left Mecca for Baghdad where a gurudwara ( Now destroyed by the IS) commemorates his visit there( 1511 AD). From Baghdad his movements are hazy, but a an inscription on a tablet at Istanbul discovered in 1994 has raised the interest of scholars. Nanak is assumed to have come back to Punjab via Persia and Afghanistan and a gurudwara in Tehran testifies to his having passed from there. But the tablet at Istanbul is off great interest.
The tablet was discovered by a Sikh scholar who visited Istanbul in 1994. The tablet it appears was erected around 1550 when the Ottoman Empire was at its peak and faces the strait of Bosphorus. The tablet has inscriptions in a language he could not decipher, but he could make out the word Al Majid Nanak. He decided to carry out further research and two men from Pakistan Punjab worked hard to decipher the script, which was in ancient Turkish and Arabic. The 2 Muslim scholars who helped to interpret teh script are Iqbal Kaiser and Syed Afzal Haider.
The script is now deciphered and reads that a great Pir from Hindustan named Al Majid Nanak came here to bestow good to the people of Turkey.This is in real terms a great revelation. But I must add that apart from this inscription on this tablet, there is no other evidence that Guru Nanak may have visited Turkey and Istanbul.
Lastly we can conclude that perhaps Nanak did visit Istanbul. There is every likelihood that he went to the seat of Muslim power at that time , Istanbul and the Ottoman Empire. Perhaps greater research in this field is called for. All in all this tablet is exciting news