Rescuers who reached a group of children trapped in a flooded Thai cave say finding them was the easy part; getting the youngsters out safely will be the real challenge.
There is no simple solution for the 12 boys and their football coach, who are being looked after by Thai military divers and an international team of underground rescue experts.
The path back to the entrance is long, cramped and at least partially submerged. It is possible some of the boys cannot swim, and all have been weakened 鈥� physically, and possibly mentally 鈥� by 12 nights underground.
Here are some of the options rescuers are mulling for reuniting the group with their waiting families.
Wait out the water聽
This is the safest and most straightforward option, but could take a long time 鈥� possibly months.
Japanese engineers have helped rig up a pumping system that is reducing water levels by one centimetre (half an inch) every hour.
If they could keep that up, it might be possible to reduce the flooding enough for the boys to walk out.
The problem is the weather.
Heavy rains are expected to lash northern Thailand for weeks, soaking through the mountain and filling up the cave as fast as 鈥� or even faster than 鈥� water can be drained.
鈥淧umping a monsoon away is not that easy,鈥� Bill Whitehouse of the British Cave Rescue Council told the BBC.
Escape through a chimney聽聽
The cave complex stretches around 10 kilometers inside the mountain, and it is possible that there are undiscovered 鈥渃himneys鈥� that could lead upwards and into fresh air.
Rescuers know there is nothing leading to the part of the cavern where the boys are currently holed up, but there could be an exit deeper inside the cave.
鈥淲e are mobilising all forces to survey the closest point to the place where children are, and are searching for a chimney there,鈥� said Chiang Rai province governor Narongsak Osotthakorn.
A course in cave diving聽
The most obvious option to lay observers 鈥� teaching the boys to cave dive 鈥� is the one most experts agree would be the trickiest and the riskiest.
It takes a healthy adult around three days to learn to scuba dive, usually in calm, clear water, during daylight and with no obstructions overhead.
The cave is dark, cramped and flooded with fast-flowing, muddy water, where visibility is sometimes only a few centimetres.
The risk of something going wrong, or one of the boys panicking and endangering himself and the rescuers, is high.
Torsten Lechler, a diving technical adviser from Germany who is assisting the rescue team at Mae Sai, said one option would be to teach the boys very basic skills, such as getting used to wearing diving equipment and breathing through masks.
They could then be guided along a swim line, with multiple stops along the way to change their air tanks and be assessed by experts.
The complex is 鈥渟nakelike鈥� said Lechler, winding up and down with steep climbs and flooded areas where there would be no choice but to dive.
These stretches are up to 15 meters long, with poor visibility or no light at all, and the group would need to rely on touch alone.
Send one child as a scout聽
If rescuers decide on the diving option, one way to mitigate panic among the boys would be to have one of them 鈥� the most assured 鈥� go first.
鈥淲hat if some (of the group) want to leave using the diving equipment and others don鈥檛?鈥� said Britain-based Andrew Watson, who has rescued mineworkers trapped by floods or fire.
鈥淛ust one individual panicking in the water could have a disastrous ripple effect.鈥�
One of the children would volunteer to go first and then pictures could be shown to the rest of the group to prove that he had arrived at the other end.
鈥淚f he can do it, you can do it,鈥� said Watson.
Floating 鈥榩ackages鈥櫬�
An alternative to asking the group to make the long dive themselves may be to 鈥渓iterally bring them out in packages,鈥� British caver Whitehouse said.
鈥淚f you imagine them in a stretcher with an air bottle, with a full face mask, and鈥� float them out through this, where they don鈥檛 have to swim themselves.鈥�
Whitehouse said the method has been done on other cave rescues, although Thai officials have so far not mentioned this option.
The cave鈥檚 passages are narrow and winding and it is not clear if floating them out is possible.聽 聽/vvp