It has a long coastline and several rivers such as the River Teifi , the River Aeron , the River Rheidol and the River Ystwyth . Large towns include Aberystwyth , Lampeter , Aberaeron and Cardigan . Other significant rivers include the River Aeron which has its estuary at Aberaeron , the River Ystwyth and the River Rheidol both of which reach the sea in Aberystwyth harbor .