A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Zero CC tileable hard cover cells book texture, 4k, scanned and made by me. CC0
Source Sojan Janso
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
The image depicts a seamless pattern which includes hexagonally-aligned gourds with BG in light-brown.
Source Yamachem
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
This one is quite simple in design, it consists of vertical stripes layered on top of a seamless texture.
Source V. Hartikainen
Feel free to download this "Dark Wood" background texture for your web site. The background tiles seamlessly!
Source V. Hartikainen