Hemp

At first, I thought to dedicate this posting to all seaside thermals on Pantelleria. But after a lot of research there's so much information to share that I will just have to limit myself to those by the name of Nicà. 
But just expect more to come. 

The hot springs of Nicà (or Nikà) are probably the best of the island's coastal thermal features. 

Five minutes drive southwards on the perimetrale road from the village of Scauri, Cala de Nicá is a nifty little cove which needs some imagination of it's visitors to see the potential. 
On the road itself are a couple of parking spots, from where it's a very steep walk down to the cove itself. 

Once coveside, your soaking solace is then to your left. Which requires a swim.

Left it is then, but there doesn't seem to be consensus on how far to the left. 

My trusty guide (Rough Guide To Sicily, 2017) says you skip a large part of the left handed swim if you throw yourself off the rocks just after the first house met, while wandering down from the main road. 
Well it actually says: 

'Punto Nikà
Signposted from the main road (where there are a couple of parking spaces), a rough lava track descends to Punto Nikà, with exciting swimming below another of Pantelleria's polychrome cliffs - this one green, rust, rose and white - in a little cove with fisherman's huts built into the rock. 
...
In summer, there is usually someone renting out kayaks, which you can paddle to a cluster of hot springs back up the coast.

It is also possible to reach the hot springs on foot, though the path is not marked. As you head down from the main road, instead of continuing to the cove, walk past the first house on your left (with metal gates), and look for a narrow path that begins 3m or 4m beyond it. The path leads to another entrance to the house, then plunges steeply downhill following a rope railing along the edge of the house's garden. As the garden ends, white arrows direct you to the bay. Note that the springs are offshore, so you need a calm day to swim out'.

Anyway, on my first visit the sea was very choppy; too choppy to even contemplate hitting the waters. Well, actually that would have been possible but it would have been very difficult getting out. And I suspected that the seas would disperse any heat from the soaks, so that might possibly result in a wild goose chase. 
Did scout the area though, found the path mentioned down (it's more like 10m beyond the mentioned first house, but you'll recognize you're right if you meet the railing pictured in lead photo below the house) and followed the arrows on the rocks.

Anyway fastforward a few days, the weather has settled and so has the sea. We walk down, straight for the soaking site. I had gathered some more info and knew that even there, the heated sea was still to the left, in the cove thing, if you like. Well, I say cove, but it's more a 10m wide inlet with steep sides. So you walk down to rocks north of this inlet and swim from there into the inlet proper.

Early morning, there were already 3 others on the little rock shelf site and our trip down brought others following, so quite busy.

Giddy on the bright day ahead, I strip for my admirers (?) and jump in and within seconds am out of sight of all others. 
I suspected that the far side of the inlet would be the hot side, it looked as such from above. But though the waters were distinctly warmer there, it were the waters on the other side which were nearly boiling. With the sea coming in and out, very hot flashes were exchanged for cooler waters, a great feeling and a great start to what would be another exhilarating Pantescan day nonetheless.

Surprise
As has become usual when seeking info on Pantelleria, there's not too much info out there in English on the island's prime sites.

Tripadvisor on Nicá: #9 of 43 things to do in Pantelleria (42 reviews: 4.5 stars). Virtually all comments from Italians, translating doesn't add much info (thank you google translate). Just one Russian contributor, who immediately gave only a single star: no place to stick the sun umbrella apparently! 
I would think differently in this case (on studding stars).

Then there's the Viverepantelleria.it website on Nicà:

'Nicà (or Nikà, the Arab word for the pools where hemp for cloth used to be soaked) is found south-west along the perimetral road. In the hunting season, hunters often surprise game that stop to drink at the pools. The "Fiumara della Serraglia" crosses the area before flowing into the "Kharace di Nicà".
It is today an ideal bathing place between a small fishing boat harbour and a hot water spring cave, protected from the north wind. The water reaches of 40°C, the good temperature for soothing phlebitis'.

Just so you know, wikipedia:

'Phlebitis or venitis is the inflammation of a vein, usually in the legs'.

Magoguide:

'Nika is a wonderful spot for a swim on a hot, summer Pantelleria day. There are even some warm springs under the water for those slightly less warm days'.

A translation from Pantelleriaguide:

'Cala Nicà: Nicà's thermal waters spill through the rocks of the coast, mixing with the sea water. The water temperature is between 85° C and 100 ° C. Like those of Gadir, Sateria and Scauri, there are no doubt therapeutic virtues. In the vicinity there are small deposits of sulfur, deposits of hydrated silica and alum'.

The inlet from above, the actual thermal sources are directly below where photo was taken.