Licancabur Volcano stands out from anywhere in the San Pedro De Atacama region and cannot be missed. It has a unique cone shape. Certainly worth for clicking pictures of same.

I did it without agency, so it's possible. However I don't recommend it to people without experience in high altitude mountains. First day you have to arrive to entrance to the park. You can take transport from SPA. There you can say that you want to climb the volcano and the guards will find you a guide and the transport for tomorrow morning. You'll spend the night in the hut close to Laguna Blanca. If you think you don't need the guide, you should make up some story and convince the guards that you'll just go to camp close to Laguna Verde or something similar. Climbing volcano is allowed only with the guide, so if you want to do it solo you'l have to break some rules. I don't recommend you to do this unless you are well adapted to high altitude and you are in very good shape. In case you do it alone, you have to walk from the entrance to the base of volcano 11km. There you can camp. Don't camp at Inca ruins! You can camp a bit lower, there's a place protected from the wind at the end of the road. I started ascent at 5:00 and was on the crater at 12:00. Bring all the water you need. For 2 and a half days I've brought 4 liters. I've lost my path in the beginning but found it later. Use the Maps.me and choose the right path, not the left one. The path is not well marked, and especially in the night it's hard to follow it. On the way back it's impossible to miss it. The views are spectacular, from the beginning. Laguna Blanca in the morning is like a mirror and then with the wind gets its white color. You'll see flamingos there. Laguna verde is the most beautiful lake I've seen in my life, and I've seen a lot of lakes in South America. The sunrise was amazing, the view from the top too. Inside the crater there's frozen lake, one of the highest in the world. The ascent is not technically difficult but it lasts for 7-8 hours. Half of that time you'll need for descent. There's a lot of wind in the afternoon but it wasn't cold as you'd expect at almost 6000m. Great experience!