Achalasia is uncommon but classic in presentation: progressive dysphagia for both solids and liquids (unlike cancer, which is solids first), regurgitation of undigested food often with bad breath, and weight loss. Diagnosis combines high-resolution oesophageal manometry, barium swallow (the classic "bird's beak" appearance), and endoscopy. Surgical Heller's myotomy with partial fundoplication is the gold-standard treatment, with per-oral endoscopic myotomy (POEM) as an effective alternative in selected cases.