St Nicolas was originally the abbey's chapel for lay folk — the abbey itself was off-limits to ordinary parishioners — and sits hard against the Abbey Gateway on the north side of the market square. The west tower and parts of the nave date to the twelfth century, which makes it the oldest standing structure in central Abingdon.
The interior is small and mostly Victorian after a heavy restoration in 1881, but the medieval graffiti scratched into the porch is worth looking for, including ship and compass marks left by river travellers. The church is usually open during the day in summer.