Taksim and Istiklal is the heart of European side of Istanbul. It's no surprise that there are tens of parallels around full of graffiti and street art awesomeness. At Nur-i Ziya Street you can find a whole section of building covered with layers of graffiti patterns by Luxury Hands.
Or just one street later at Eski Cicekci Street there is the famous Leo Lunatic panda waiting to surprise you. Many car park owners allow artists to cover all inside and there are very surprising spots not to miss as well.