Yes. To hike the final trail (Trail 10, Telesforo Bravo) from the upper cable car station to the absolute summit, you need a free summit permit. These permits are in high demand and should be booked 2-3 months in advance. The cable car ticket does not include this permit.
You must wear layers. Even on a hot day at the coast, temperatures at the 3,555-meter summit can be near or below freezing. A fleece or windproof jacket, a hat, and gloves are strongly recommended. Sturdy, closed-toe footwear like hiking boots is mandatory; sandals and flip-flops are not suitable.
Expect significant temperature drops. In summer, temperatures at the upper station are typically between 8 °C and 15 °C. In winter, they can fall below 0°C, and the wind chill will make it feel even colder.
From the top, you get sweeping views of the mountain's own volcanic craters and unique plant life. On a clear day, the vista expands dramatically across the Atlantic, allowing you to see the neighbouring Canary Islands of La Gomera, El Hierro, and La Palma on the horizon
Yes, the high altitude and clear, dark skies make it an excellent location for stargazing. The provided text notes the importance of this, advising visitors to turn off vehicle lights at night in viewpoint parking spots to avoid light pollution and protect the pristine viewing conditions.