A day trip to Lake Como is absolutely worth it, provided you focus on the "Mid-Lake" region. Most travelers take the 40-minute express train from Milan Central to Varenna-Esino. Varenna is widely considered the most beautiful town on the lake and serves as a perfect hub. In a single day, you can walk the "Lovers' Promenade," visit the gardens of Villa Monastero, and take the 15-minute public ferry across to Bellagio. While you won't have time to see the entire Y-shaped lake or visit the city of Como itself (which is actually less scenic than the northern towns), the "Golden Triangle" of Varenna, Bellagio, and Menaggio is perfectly manageable in 8 to 10 hours. The key to a successful day trip is using the "mid-lake shuttle" ferries rather than the slow boats. While you’ll leave feeling like you’ve only scratched the surface, the sight of the snow-capped Alps reflecting in the deep blue water and the grand neoclassical villas is a high-impact experience that justifies even a short visit from Milan.