Both. Pyramids, gravity, Indian temples, stone henge, the patterns in the universe, cells etc. Like one simple example near where I used to live - the architecture of the Konark temple where it had a sort of magnet to levitate the "vigraha". The magnet was at least ~50 tonnes. http://www.thekonark.in/konarkfloatingidol.html
Another temple where the pillar does not even support the temple's roof: https://www.indiatimes.com/culture/travel/this-temple-has-a-...
Musical pillars made of stone. http://www.themysteriousindia.net/singing-pillars-hampi/
You may baulk at these, because your perspective is from probably an arrogant modern scientific outlook, but these buildings & structures predate even the pyramids. Many just too many of these have been destroyed by religious fanatics who cannot tolerate an alternative mode of thought besides Islam & Christianity, so what survives is a sorry remnant of that era, which even so is impressive I think.
> Fundamental understanding
Contingent upon a perspective of ignorance. Is that not correct?
For example, we use light as a form on energy in lasers etc, but only 70 years ago, this would have NOT been a fundamental understanding. The problem is that most of today's people, except the really great people like Einstein, Hawking, Heisenberg, Schroedinger, Tesla etc, try to dismiss (& worse appropriate) any sciences that simply originated in the Indian subcontinent, and I am not sure why that is the case. Why do you think every major civilization in the last 500-600 years wanted to find a path to India. Why do you think the American native people are still called Indians? Why do you think strides in Science & Math were monopolized in the Indian subcontinent & it required the onslaught on the Islamic hordes first and then the European / British hordes to stop the progress of all such advancements? You may not be aware that the industrial revolution of Britain & Europe was funded by India & Indian wealth. Anyways, I digress. My point is that "fundamental understanding" is not limited to a set of people, it just requires time & since India is part of the longest surviving civilization (even the face of 80% destruction) there is a lot of understanding we can acquire from what the rishis had accomplished. We should not throw them all away just because we cannot make head or tail of it...