For more than a hundred years after that, mountain guns proved useful at the margins of various wars, often being taken to bits and lugged around on the backs of mules.

Unfortunately, it can take a long time to get up the mountain this way, and meanwhile you and your mule (and the goat) are (nowadays) vulnerable to snipers. So, for a generation now, fire support in places where big tracked vehicles can't go has been provided by helicopter gunships (OK, and planes too).

But with helicopter gunships you can hear them coming, you can see them coming and their armour is limited by the fact that they have to fly.

Hence I propose a thing like a giant robotic spider packing a howitzer. Most of its fuel, ammunition and probably crew could be carried in a separate tender vehicle (perhaps also with spider legs, but maybe shorter ones). This separation would enable the tender vehicle to hide in a nearby crevasse while the monstrous spider reared up over a ridge-line and took a few shots, before scuttling off in the classic 'shoot and scoot' style.