No, the HavaIST is an airport shuttle bus, but you can connect with the sightseeing Big Bus at all major tourist attractions. If you’re on a layover, you can take the HVIST-14 directly to Taksim Square where you can easily walk to Iskital Street or the Galata Tower. For Sultanahmet, the closest option is the HVIST-12 to Beyazit Square, which a 1.5 km taxi ride away from Hagia Sofia, Blue Mosque, and Topkapi Palace. If you wanted to see Dolmabalche Palace, the HVIST-13 will drop you off just a short walk away at Bakirkoy Pier.