South of Arecibo, its outlying suburbs tier upwards into the hills, then peter out entirely into swooping forested peaks and ridges, where the rock is riddled with cave systems. You can make the transition from coastal city clamor to mountainside calm in little more than a 20-minute drive, and this fact renders the region the most visited of any in the island's interior.
Headlining a string of blockbuster sights here is the world’s largest and most sensitive radio telescope, the Observatorio de Arecibo. Harboring a fascinating museum and a view worthy of a futuristic James Bond film set, the observatory is open for public viewing and reigns as one of the island’s most rewarding must-sees. There are also rugged forest parks, spectacular caverns, boat trips on lakes and a host of other adventures nearby.