So yeah ... if you fancy witnessing the above for yourself then here's how.
You're going to need:
1 x SRV
1 x AMFU (optional)
1 x corrosion resistant cargo rack (optional)
1 x normal cargo rack
1 x Guardian item of your choosing (later)
1 x Thargoid Sensor (later)
1 x Thargoid Link (later)
The good news is that you don't need a Thargoid Probe (unless you also want to see the Thargoid Machine's planetarium lightshow). This is good news because they're a pain to get hold of while all the other stuff is pretty easy.
First of all head off to one of the Guardian ruins. There's a list of them over here:
Bear in mind that your next stop will be HIP 17403 so pick one of the systems that's closest to that (sorry, don't currently have an optimal suggestion).
When you get there and have landed at the appropriate co-ordinates ..
n.b. this might come in handy!
Next head to the Thargoid crash-site in HIP 17403 on planet A 4 A at co-ordinates -34.9831, -141.4127. Deploy the SRV and go and scoop up a Thargoid Sensor (they're lying around making spooky noises near the core of the alien ship).
Now, this thing will corrode your ship. There are three ways of dealing with that.
1) do the next bit FAST!
2) carry an AMFU and use it to make damn sure the integrity of your cargo hold doesn't drop much below 75% (otherwise all your cargo will fall out and you'll be back to square one).
3) do the whole Palin engineer rep' grind thing and get yourself a corrosion resistant cargo rack
I guess I'd recommend option 2 unless you already have the Palin rack.
Now fly to an "active" Thargoid base of your choice. There's a nice interactive 3D map of these over here (the "active" sites are marked in red):
Land at the site, deploy the SRV and transfer your Thargoid Sensor and your item of Guardian tech into its cargo hold. Drive to one of the circular iris-doors in the outside of the base and say "open sesame" (actually, it's having the Thargoid item in your cargo that causes the door to open). Drive inside and navigate your way to the Thargoid Machine in its central chamber.
There you'll see three sparkly holographic images, each with a strange kind of alien ramp leading up to it. When you drive up the ramp the hologram in front of it resolves into an image of the thing it wants.
Find the one for the Thargoid Sensor, drive up the ramp until you're parked directly over the green hole and then jettison the Sensor into it. The hologram should disappear and the Sensor should end up dangling in its place on a piece of Thargoid Thread(TM).
Now find the hologram for the Thargoid Probe and jettison the Guardian item in its place.
Lastly you need to go and grab a Thargoid Link. Drive back to the circular outer passageway and take one of the exits that leads down rather than up. At the bottom you'll see three Thargoid Alcoves(TM). Drive up to one and a Thargoid Link should drop down from the ceiling above you on more Thargoid Thread(TM). You should NOT fit the Thargoid Link over either your own nose and mouth nor those of any children sitting next to you.
Simply scoop it up and drive back to the central chamber again.
Note: if a tendril drops down from the celing but has no Thargoid Link attached to it then you've hit what I suspect may be a bug (I'm afraid this happens quite often). The easiest way to fix this seems to be to mode-switch (i.e. log out to the main menu and then log in again in a different mode). For safety I took all my stuff back to my ship and flew to a safe distance before doing this. This was a pain in the butt and may not actually be necsssary.
Once you're back in the central chamber jettison the Thargoid Link into the final hole and then retreat to a safe distance ('cos some serious shizzle is about to hit the fan).
Scan the Thargoid Machine!
Note #1: The scavengers will turn ugly and start to attack you so probably best to deploy the SRV's turret and pick them off before settling back to take any selfies. Probably a good idea to set full pips to shields once you've dealt with the scavengers too!
Note #2: All three items will ultimately be destroyed by the machine!
Addendum: How to see the Thargoid Machine's planetarium lightshow!
OK, so for this you're going to need a Thargoid Probe which is slightly trickier to get hold of.
The method I recommend is to just keep dropping into Threat Level 5/6/7 NHSS (non-human signal sources) while flying around the Pleiades in Supercruise. As soon as you drop into normal space fly towards any debris you see and check your contacts panel. If there's no Thargoid Probe listed then get the hell out of there asap. If there is then you need to scoop it up quickly (I guess using a Collector Limpet to grab it is another option).
Note: you might have to visit a dozen or more instances before you find one.
You may well run into Thargoid ships while doing this so it's best not to be carrying anything that excites them or they might attack (I lost a Python on my first attempt because I was already carrying a Thargoid Sensor).
For this reason I recommend changing the order you collect things. So get the Probe first, then the Sensor (from the crash site), then some Guardian tech. Unfortunately this makes the journey a fair bit longer (Thargoid space for Probe and Sensor, then Guardian space for Ancient ruins then back to Thargoid space for the base) and also means you'll be carrying corrosive cargo for longer!
Once you've got a Probe, a Sensor and a Guardian item head to the base as normal. First of all take the Probe and the Sensor and put them into their respective slots. Then go and get the Link and drop that into the last slot. Proceed as before and witness the lightshow (which does not destroy the items but simply pops them back out of the machine at the end). Now you can go back to the ship (remembering to take one Thargoid item with you to open the door