Question: I've been reading through other posts about such megastructures and they're getting me part of the way to my destination. Wanted to see about a few specific options my imagination has latched onto.

The original concept is a tower, an arcology with a 1 km base level (willing to taper it as it gets higher if necessary), reaching to at least 8 km altitude. 

Assume that available power is not an issue.

One idea is: Blocks, rectangular or triangular prisms, containing powerful electromagnets that are the 'mortar'. I liked this option because the society is ancient, and a blocky look fits the aesthetic better, masking the futurism. I realize it is power inefficient. Would such a thing work on this scale?

Thanks!

EDIT to reflect excellent comments: 

Trying to avoid elegant solutions such as Space Fountain, Space Elevator, etc. We want to solve the issue of structural stability with brute force as much as possible. Would a system like this hold up versus gravity, bending and torque at high altitudes?

Answer: 
Easy peasy. Basically, you want lucid dreaming with an I/O interface.

(Note: If I can dodge work enough I will try to find the New Scientist sources for this to add to the answer later, but I have read articles on all these three points recently)

You simply need to rig up a brain interface into the optic nerve. There is recent technology that can show a grainy but identifiable image of what someone is looking at simply by measuring brain waves; that gives you the output part. 

The input part you'll have to handwave, but it's not too much of a stretch to come up with something that can trigger specific images.

As for the immobile part, that's exactly what the body does naturally during REM dream sleep. So simply plug in your I/O helmet, trigger the body's natural REM state to immobilise your muscles, boot up the lucid dream for the world you want, and voila!

This addresses the comments I've seen here a few times - about the difficulty of immobilising muscles, and about fast/fine control; I have incredibly vivid, occasionally lucid and almost always sci-fi dystopian dreams, and I can confirm that I can walk, run, jump, fly, fight, drive vehicles, fly planes etc etc etc and all without falling out of bed, and I'm pretty sure everyone else here can too :)
Using some logic from Ghosts of Onyx from the Halo series, a rebel general manages to attach a disruption collar to a set of spartan armor which halts all commands to the suit basically rendering them immobile. Perhaps the same could be applied.

What I would propose is a motorized suit that is linked to the helmet. This product is, unfortuantely, less of just a helmet and instead a fully enclosed, articulated and motorized suit. It would have to be fully enclosed in order to create the immersion necessary to feel more in the simulation. The suit would take data from both the user and the simulation. It would allow freedom of movement within the limitation of the simulation. The suit would instead translate interactions by using the motors (or hydraulics or any method of artificial locomotion). An example would be walking into a wall. the suit would limit the range of motion the user has at the moment they interact with the object. Another, more dynamic example would be wrestling with an opponent stronger than the user. The suit would simulate this by actively resisting or even moving the body in the same direction as the simulation dictates the opponent would push it.

To increase immersion, the inside of the suit could be lined with numerous small hydraulic pistons on the inside, nothing dangerous or large but just enough to jab someone inside. For example, walking into a table edge would cause 1 or a set of the pistons to strike you at or near that location causing a real sensation of discomfort. It would help discourage the user from making the same mistake as the simulation now contains real life consequences.

To help with climate or other sensory inputs, a mesh could be worn beneath said suit that can produce both heat and cold sensations. Depending on the intricacy of the suit being worn, it could simulate temperatures in specific places only. This would only apply to things like the user sticking their hand into a fire in the simulation or taking a plunge into water.

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> they would control their own body, without also moving their own body.
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This part would be difficult with this suggestion as it would require a range of motion. Though perhaps creating some sort of suspension device attached to a suit would allow this.

Though, if I may add some pros and cons to the suspended suit suggestion

**PROS**

* allow for non invasive feedback from the system in terms of trauma or resistance
* allow unmodified personnel access to the simulator
* reduce the amount of time needed for tedious tasks (cleaning ports, maintaining ports)
* reduce need for surgeries to maintain any implants (should be none with this method or minimal)
* total system failure or feedback would most likely not kill the user (feedback levels allowing of course)

**CONS**

* requires an area for range of motion
* Possible suspension devices hampering motion
* increased device maintenance
* requires a fully enclosed, possibly air tight helmet for full VR immersion (may lead to suffocation for failures)

Edited for clarity.