Mt Yasur - also known as Tanna Volcano - is one of the world's most accessible volcanos. There are two ways to visit the volcano, as I will outline below:

Mt Yasur Tours

This is the information you will find online. It costs 8000 vatu to enter the volcano on foot, or 10,000 vatu to be driven up to the crater. 

The hike from the gate to the crater takes 45 minutes along the (mostly) dirt road. It's actually a beautiful walk, and I've done it four times with joy. There are some steep bits, but it's not straight up the whole way. The volcano is only 360 metres above sea level, and the path snakes up the side. 

If you want to be driven up, the drive takes around 10 minutes and costs an additional 2,000 vatu, or 10,000 vatu in total. From the top of the carpark it is only a 5-10 minute walk up to the rim of the volcano. You can either do the tour before sunrise (4am) or before sunset (5pm), as lava isn't visible during the daylight. The number of people visiting each day does vary - with significantly fewer people during cyclone season (November - April) due to the logistical difficulties of Vanuatu and likelihood of flights being cancelled. During peak travel times, such as Australian and New Zealand school holidays, you're also likely to see more people up there. Other times there may be as few as 10 visitors to the volcano. 

Climbing it Yourself?

Strictly speaking, it is illegal to climb the volcano by yourself. It is also dangerous, and potentially stupid to go up an active volcano in the middle of the night. If you're going to do this though, at least be smart about it. Speak to a local about this first. If the local trusts you, believes that you will respect their sacred site, and thinks that the conditions are safe enough, they may invite you to climb it yourself. If they tell you no though, do not push it. 

The family that owns the volcano charges 8,000 vatu per person to visit the volcano, although many of the surrounding families and villages disagree with this price. Some other locals may offer to tell you how to get up the volcano safely. Speak to your treehouse or bungalow host before you go up solo. They will give you honest local advice. If there is increased security on the volcano, they will tell you. If the volcano is reaching Warning Level 4 (Major Eruption), they will let you know it is not safe. And importantly, if something happens to you, they will know to sound the alarm. If your host doesn't want to discuss you climbing the volcano yourself during the night, then simply don't go. It is an active and sacred volcano, so respect what they tell you. If you are visiting the volcano by yourself, you should be invited to do so by a local. If you do not receive an invitation, please stick to doing a tour. 

There are two ways to climb up and your host will talk to you about which they recommend on the day. The first is to go to the ash plains at the base of the volcano and climb straight up. If you've ever climbed a massive sand dune before, you'll know what to expect. It is 30-45 minutes of straight ascent, and for every metre you climb, you'll slip back at least half a metre. You'll also be facing directly into the ash dust, so bring a scarf to cover your mouth and night-appropriate eye protection. Lasty, be careful sliding down on the way back. It's tempting to slide the whole way, but the volcano is covered in rocks and this is a sure fire way to hurt yourself. 

The other option is to go around the guard tower at the entrance and follow the road up. To get here though, you would need a local who is willing to show you the path as there are no direct paths without crossing through peoples' homes and villages. Most locals live in hand made houses and have guard dogs, and if you attempt to sneak through here without permission you will get caught, you will scare the people trying to sleep, and you will set off a hundred barking dogs. Many of the locals in this area are happy to guide (friendly) travellers through to the road up, but do not expect or demand to be invited up. This is their home, the volcano is sacred, and your desire to get up to the volcano is not a right. If you are genuinely friendly and not demanding, you may be invited. 

The benefits of travelling up to the crater by yourself is that you can stay there for as long as you want. Do keep in mind though, there are no safety rails, and large plumes of sulfur accompany each eruption. This can be lethal and very dangerous to breathe in.