The place on the video is Yalahar Zoo +1. You need some requirements to get to Yalahar though... which means you will need to do firstly some tasks.
The Way to Yalahar
First make sure you are a member of the Explorer Society and have the rank of novice or higher, otherwise you will not be able to talk to Captain Max in Liberty Bay. 1
For the better view of maps of the above pics visit Tibiopedia.pl 2
Another place where you could find single Behemoth would be in North-West part of Tarpit Tomb on -7.
So well, there is a cave with one Behemoth in Liberty Bay (Vandura Mountains- Wyrms respawn. However, as you are RP It will not be preferable as the cave is super small and there is no space to run (and I am sure you seen it)... It is on level +6. Also on the way there you will face many Wyrms. Also on +7 there is spawn with two of them, but yet again- it is narrow.
On the same level where single behemoth respawn is, as you already mention, you will find few more Behemoths. Possibly it would be a good idea is to drag (not kill) most of them on the end of the spawn and focus on one of them? I would actually recommend you to ask some EK to keep the behemoths occupied while you doing your solo:) There is always someone ready to help!
Spawn marked here:
And of course... you can try Serpentine Tower ;X