I’ve visited Ethiopia a few times and twice managed to be at Lalibela for ‘Genna’ and the scene is truly awe-inspiring. Around 100,000 pilgrims, largely the rural poor, many of whom have walked for weeks, often barefoot, arrive to celebrate the Ethiopian Orthodox Christmas. As the local villagers feed them, they camp where they can, often sleeping shoulder to shoulder on whatever bare patch of rock has not already been taken. You can read more about it here.
I trekked across Tigray, up near the border with Eritrea, visiting the numerous hidden mountain top monastries and cave churches. It happened to be wedding season when I was there which made progress slow as it was insisted that I joined in the festivities along the way.