Arrive at least 10 minutes before your chosen time slot. From Termini, take Metro A (direction Anagnina) to San Giovanni, then bus 218 (direction Ardeatina) and alight at Fosse Ardeatine — the entrance is directly in front of you. Alternatively, take Metro B (direction Laurentina) to Colosseo or Circo Massimo, then bus 118 (direction Appia/Villa Dei Quintili) and alight at Catacombe di San Callisto (Via Appia, 110).