There are a couple of filters that are ideal for images like this: a straight Neutral Density (ND) filter or a polariser.
Neutral Density filters are available in various strengths, and a two- or three-stop version is perfect for reducing the light enough to use a 0.5 sec shutter speed in most lighting conditions.
A polariser, meanwhile, will increase saturation in your shots, but it will also reduce the light by up to two stops, so can be very useful in bright conditions.
It’s not exactly a new technique, but shooting infrared images can give you a new view of a familiar landscape. You’ll need a sunny day so that there’s plenty of infrared light to record, and some fluffy clouds in a blue sky are ideal.
To get the full infrared effect you’ll also need an infrared filter. These are almost completely opaque, and only allow a tiny amount of visible light to pass through them.
Gauging the exposure will take a bit of trial and error, as not all metering systems and sensors have the same sensitivity to this type of light. So shoot in Manual exposure mode and use the settings suggested by the meter as a starting point.