This paper presents the ALBA Project (Ancient Legacy Bayesian Assessment), which identifies a candidate archaeological site at P5 (7.550°N, 117.750°E, Sulu Sea) matching Plato's description of Atlantis across ten independent quantitative parameters, through a systematic four-stage Bayesian investigation. Stage 1 evaluates geological, archaeological, and acoustic evidence for a technologically sophisticated yet non-industrial civilisation prior to the Younger Dryas cosmic impact (~12,800 BP), designated hypothesis H₃, raising its posterior probability to 45–62%. Stage 2 identifies a recurrent technological fingerprint — golden-ratio (Φ) geometric placement, proximity to geological faults, use of piezoelectric/electromagnetic materials, and association with mercury deposits — and deploys it as a predictive search tool. A global Φ-scan isolates P5. Stage 3 validates P5 against independent evidence lines: philological analysis of Plato and Herodotus, Egyptian directional inversion, GEBCO/GMRT bathymetric matching (RMSE = 6.2 m for the concentric ring system 2.5:1:2:2:3:3 stades), myth-bathymetry correlation (Nunn method), population genetics (Sama-Bajau), and the diasporic triangle. Stage 4 subjects the Φ-signal to a Monte Carlo self-audit — retracting initial Bayes Factors from 200–500 to 10–25 and uncovering a hub anomaly at z = 4.98 — then examines convergent signals including the Nazca Convergence (p = 0.00017) and archaeoastronomical analysis of Betelgeuse mythology across five continents. P5 satisfies 17/20 criteria. Final posteriors: P(H₃) = 90–96%; P(P5) = 88–95%. Three criteria require direct underwater investigation at −19 m depth. Preprint — not peer-reviewed. The authors assume full responsibility for the content. Comments, critiques, and proposals for collaboration are welcome.