A massage before your flight or after you land. In-airport spas sit past security, so you need a boarding pass for those. Nearby studios are by the airport hotels and take walk-ins where shown. Distances are straight-line miles from the airport. Many in-airport spas accept Priority Pass for one treatment.
In the airport
Near the hotels
Prices change. Verify the price and hours with the spa before you go. Where a spa publishes no price, the card says so. LHR prices are in GBP. In-airport spas are past security and need a same-day boarding pass.