High Dynamic Range Imaging is a great way to spice up your scene fast.
HDRI Haven
HDRI Haven is one of the Haven game asset sites offering different assets for games with up to 16K resolutions.
HDRIMaps Freebies
HDRIMaps website offers a variety of textures and HDRI maps for different sceneries. While most of them come with a cost, there is a noticeable amount of freebies offered in their site.
