The NASA images as16-121-19407 and as17-150-23085 are in fact both of Lobachevskiy crater (note the correct spelling).
You can see that the Apollo 17 photo is of Lobachevskiy crater by comparing it to the Lunar Reconnaissance Orbital Camera (LROC) data available here . (You may want to turn on names by clicking the Location Overlays item from the Layers menu on the left, and then clicking Moon Features - sorry, but the permalink doesn't remember those settings. You may also want to turn off the false colour elevation data by clicking the LROC WAC Colour Shaded Relief checkbox second from the bottom in the same Layers menu.) Remembering that the A17 image is upside down, you can see that the central peak, the bright fresh crater just east of the central peak, and the relatively fresh crater on the southern rim of Lobachevskiy are all present in both the A17 image and the LROC data.
The A16 image is also of Lobachevskiy. Again, comparing it to the same LROC data (you may need to zoom out a bit) you can see an irregular crater (with a large crater taking up a quarter of the south-west interior) to the north-west of Lobachevskiy in both the A16 image and LROC data. So this means that the write up of the A16 image here is unfortunately wrong (sorry, it happens sometimes when you have thousands of images to describe).
With that out of the way, we can take a look at this feature in very high resolution data by zooming in on the LROC data. To make life easier for people, I have done that for you here (again, you may want to turn off the LROC WAC Colour Shaded Relief checkbox). You can get your bearings on where this is in Lobachevskiy by zooming back out and then in again. It is clear from this data that there is no tower, cross, or tunnel entrance here. This is simply a crater that formed on the walls of Lobachevskiy crater. The steep slopes forced all the melt from the small crater to flow downhill. You can see a stunning example of one such melt flow across the bottom half of this crater. On the east side of the crater, much of the melt pooled, forming a slightly smoother area. From there, some of the melt spilled over to form long dark flows, which certain people have mistaken for a tunnel entrance in A17 and the shadow of a tower in A16.
I hope that was helpful. If nothing else, I would encourage people to browse around the LROC Act-React Quick Map. It really is a great tool for looking at the Moon (both in high resolution and more regional views). It's used by many lunar scientists and engineers, but is also very user friendly, making it great for the general public too.