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Quite expensive, considering the hot spring along the Salar de Uyuni tour is just Bs. 6. There are other (private) hot springs nearby, try this hot spring or this one. From the latter a trail north leads to two more hot springs, which might be for free.
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A little cheaper and free if the lady is not there. So, go early or late (coming from the Tres Lagunas Trail), or just be lucky (e.g. in off-season).
Wisalla
This medium-difficult peak provides amazing views of Nevado Sajama, Sajama village and the surrounding plains. Due to the high altitude it can be a day trek, the higher you get, the harder it will become to progress. Take your time! There is a trail that goes almost straight up from the village, or you choose the longer one that circles the mountain to the east and then offers a less exhausting final trek at the end.
Surprisingly versatile with hot pools, geysers and mud pools. It also has some little and free and natural pools you can soak in—just select a place in the river that has reasonably much space and is hot enough. But also, check out you map app to find them. The very first pool is already great for a dip. (Control the heat of pool with rock near small waterfall, which blocks the water to the geyser. You can help making the pool bigger & deeper, namely where the water is calm and the hot geysers are. Maybe even bring a shovel, but do not tell the locals about this secret place, or it will be gone soon. Allow for enough cool water to flow by outside of the pool. And watch out, the soil can be very hot.)
This is the little hill right east of Sajama village. You can see the trail clearly, which goes straight up the hill. But only do it if you are not going to do Mt. Huisalla right next to it north, which has much better views.
Huanakota
A great place to see birds like the Andean avocet, the Andean lapwing, the horned coot, the ruddy duck, the cattle egret, the Puna teal, or the yellow-billed pintail.
In case you are taking your time with the Tres Lagunas Trail and camp overnight, you might in addition consider this interesting and exciting side-tour with magnificent views of the Lagunas, into the Sajama valley as well as Nevado Sajama itself. Allow for an extra day and night to conquer this mountain, but camping near the Laguna Chiar Kkota is very picturesque and convenient at the same time. In winter, the trail can be impassible.