An Ayutthaya day trip from Bangkok is completely doable (and easy) all on your own! We left from our hotel near the Sutthisan Metro Station in Bangkok and headed north to Bang Sue Railway Station where trains depart for Ayutthaya every hour. Approximately two hours later, we arrived at the Ayutthaya Station, walked directly west to the ferry, and rented bikes across the river (rental bikes are 50 baht for the day on this side, and you do not have to pay extra to transport them on the ferry). The rest of the day was spent meandering through the expansive Ayutthaya UNESCO World Heritage Site, quite possibly the best temples in Thailand. We visited four main sites (Wat Mahathat, Wat Ratcha Burana, Wat Phra Si Sanphet, and Wat Chai Wattanaram), but there are countless more that you could spend multiple days exploring. Most temples have an entrance fee of 50 baht, but we attended during the holiday period and were lucky to have free entry!