If you have extra time, you might want to visit the Janardana Swami Temple, which is only 5km from Varkala Cliff Beach. An alternative adventure option is to bungee jump at Varkala Bay.
If you have less time, you might want to skip kayaking or trekking and just enjoy the water sports at Varkala Beach as they are within reach. Or just witness the beauty of the Varkala coast at sunset from the cliff beach.