Indoor archaeological sites are particularly adapted for ground-penetrating radar (GPR) surveying because the environment is uniform throughout the year.This makes them excellent for the application of meticulous three-dimensional surveys under repeatable conditions. The objective of this work was to test different dense grid strategies and three-dimensional imaging techniques in order to improve detection of subfloor targets. Application of the isosurface rendering technique to pseudo-three-dimensionalvolumesresultedin an efficient methodology to mapthe target inthis particular case. This work shows a case history carried out at the convent of Santo Domingo (Lugo, Spain) where a sarcophagus was found.