It depends what kind of tourism you like ,historical-visit or as you mentioned beach.
If you like beach April is not good season for sea in Turkey ,its not warm enough.
But for others its good timing ,you can enjoy your time in Istanbul.
There are many beachs in & around Istanbul i think our friend doesnt have enough info about Istanbul for example Kilyos, Şile, Adalar or Çiroz, Güneş Florya
Kindly visit following web sites that you will have more info
It depends what kind of tourism you like ,historical-visit or as you mentioned beach.
If you like beach April is not good season for sea in Turkey ,its not warm enough.
But for others its good timing ,you can enjoy your time in Istanbul.
There are many beachs in & around Istanbul i think our friend doesnt have enough info about Istanbul for example Kilyos, Şile, Adalar or Çiroz, Güneş Florya
Kindly visit following web sites that you will have more info
http://www.tourismturkey.org/
http://www.goturkey.com/
http://www.kultur.gov.tr/EN/ana-sayfa/2-0/20110127.html