Pilgrimage is as old as religion itself. It is encouraged in Abrahamic religions, but is a core activity in ancient religions like Hinduism, where there are pilgrimage sights dotted all over India (with some lying as far away as Afghanistan). These are like mini quests; you can do this mission where you visit the 11 Krishna sites, or this another mission where you have to reach these 15 sites, but they are all on mountains, and you have to walk 10k steps to reach there...

AFAIK I know it is a "core activity" in one Abrahamic religion (Islam)—more so than in any other major religion.

A lot of Christians I know have done some sort of pilgrimage. Quite a few Buddhists too (most of those I know if you count short and easy trips).

I agree it is very common, but I cannot see a correlation between how ancient a religion is and how important pilgrimage is within in it.

Before the destruction of the Second Temple, pilgrimage was an important part of Judaism as well.

Thanks. It explains some things that were puzzling me about what I had read about pilgrimage in Judaism.

There are quite a few Muslim peoples who don’t recognize the hajj to Mecca as an obligation, such as Nizari Ismailis and Alevi-Bektashis. Even in the Balkans or West Africa among Muslims who ostensibly subscribe to a more “orthodox” Islam, though they might see the hajj as a nice thing, consciousness of it as an obligation may be low.

Wouldn't not believing in the Hajj be equivalent to blasphemy, which in turn is equivalent to being killed in the name of Islam?

Not if all the Muslims around you also don't believe in the Hajj. Orthodox Muslim belief is highly rigid today, but the medieval era there was a time and region when Muslim concepts could be questioned and given some mystical revision instead. That is where Nizari Ismailism (and the Druze who don't even regard themselves as Muslim any more) came out of.

There's a big difference in Christianity between Protestants and, for a lack of a better word, the Apostolic Churches (Roman, Greek, Oriental).

The later have a very rich culture of pilgrimages.

As a protestant, I fully plan to visit Wittenberg some day as a sort of pilgrimmage.

You're basically reaffirming that religions and religiosity change a lot over time. As faith waxes (no matter the religion) more will go on pilgrimages. I think historic holy sites are rad personally, even though I am not currently religious.

Pilgrimages were still a big thing among early Christians.

For example, in Acts 20:16 it notes how Paul was trying to be in Jerusalem for Pentecost. Now this was around 55 AD.