With the previous entries, I tried to show that the evidence for the particular structures or artifacts either were not what they were claimed to be by alien astronaut promoters, or the context of those items was far better explained as what we expect from humans.
The Nazca Lines: Not great as an alien space port, but it seems to best fit into local water deity beliefs and rituals. Not high-tech, probably not astronomical, but what we expect from humans with certain religious/social traditions.
The Baghdad Battery: Probably not actual a battery, and even if so it's far too low a voltage to be alien tech. Most likely it was an accidental combination of materials, and there is no evidence that such a device was used, nor that there was the know-how to have this technology. Since there is no evidence of the use of electricity at the time, nor do we find needed things such as wires for electricity to get passed around, we likely don't have something technologically out of place.
The Piri Re'is map: Rather like other maps of the time creating continents based not on ancient knowledge by philosophical musings. Doesn't actually show the continent of Antarctica, and the only way it does is if you change it to fit your conclusions. This is a case of the eye of the beholder getting in the way of what is really there.
There are many, many more things that could be pointed to and talked about, such as the moai of Easter Island, the structures at Nan Madol, Tiwanaku, and of course the Giza pyramids. However, there is a pattern that emerges all too quickly from how all this is argued by ancient astronaut folks: with a minimum of context and information about the given items, could aliens be a possible solution? Logically, there is not a contradiction in aliens built X, but possibility is a far and long shot away from probability. As Bible scholar F.C. Baur put it, "Anything is possible, but what is probable?"
And it's the same today, and I will show that to some degree in my talk as well. So, if you were expecting me to find ETs this way, that won't be happening. There are much more likely avenues to discovering life outside the earth, both with robots like Curiosity and with SETI. But I will have to explain how later.