Ayutthaya is just north of Bangkok, so it is an easy day trip.
From Bangkok
Trains from Hua Lamphong/Krung Thep Aphiwat and minivans from Mo Chit reach Ayutthaya in about 1.5 hours; organised day tours include transport and a guide.
From Pattaya
Route via Bangkok, or take a private car/tour that combines both. Allow a full day.
Getting around
Hire a bicycle or tuk-tuk at the station — the Historical Park is compact and flat.