Cycling Angkor is one of the best ways to experience the temple complex for visitors who are reasonably fit and comfortable on two wheels. The "small circuit" — about 17 kilometres covering Angkor Wat, Angkor Thom (including the Bayon, Baphuon, and the Terraces), Ta Prohm, and Banteay Kdei — is manageable in a day and gives a completely different experience from tuk-tuk touring: you can stop whenever something interests you, take side roads into the forest between temples, and spend time at smaller sites that tuk-tuk circuits often skip.
Bicycle rental is available from dozens of guesthouses and dedicated rental shops in Siem Reap from around $2 to $5 per day for a basic bicycle; better bikes with gears cost more. Start early — the heat by midday is serious and the temple crowds peak between 9am and noon. Bring water, sunscreen, and a small lock. The roads through the park are paved and mostly flat; the only significant incline is the path up Phnom Bakheng. Do not cycle to Banteay Srei (25km each way) — take a tuk-tuk for that excursion.