Yes, you can still book the Salkantay trek even if only circuits 3 and 4 are available at Machu Picchu.
It’s best to book at least a few months in advance, especially during peak travel seasons. This will give you the best chance to get access to Machu Picchu Circuit 1 or 2.
The 4-day trek is tougher because there are fewer breaks, making the daily hikes more intense.
It can be challenging for beginners because of the high altitude and long days, but groups usually have a mix of experienced and less-experienced hikers.
Many people book a few months ahead to make sure they have the best Machu Picchu entrance. Prices typically range between $350 and $600, varying by tour provider.
The Salkantay trek is generally well-received for its stunning scenery and unique adventure. Also, compared to for example the Inca Trail it is a lot cheaper. Therefore, a very popular alternative trek to Machu Picchu. In addition, it doesn’t require a permit as for Inca Trail. So technically, it can not sell out. Tour operators’ groups might be full though.
It’s best to have high hiking boots since the terrain can be slippery and muddy.
The 5-day trek is more relaxed and worth it for the extra day. You can visit Machu Picchu in this order:
Circuit 4 + Wayna Picchu
Circuit 4 + Huchuy Picchu
Circuit 3 + Machu Picchu Mountain
Bring enough cash for snacks, (warm) water, electricity, and tips. It’s better to have too much than too little since there are few ATMs.
You can leave your main backpack at your hostel and bring a small daypack for the trek. Also, most tour operators offer the option to store it at their office, while doing the trek.
The Inca Trail is more historical, with many Inca ruins, while the Salkantay trek is more about nature and landscapes. The Salkantay trek is also physically tougher.