When I visited Llansteffan Castle (CADW site) several years ago it was pouring down with rain and I approached from the north via Church Road.
If memory serves me right it was a steep walk up to the castle along the footpath but the coastal views to be had when you reached the castle made the effort well worthwhile.
I must admit that I didn’t know anything about the site being of prehistoric origin but given its location it is hardly surprising.