'The World of Tomorrow' (1980) book cover

In his popular science book "The World of Tomorrow", first published in 1980, Robin Kerrod depicted life as it might look in the 21st century. Today, living in the third decade of the 21st century, this depiction might seem overly technologically optimistic (like most past attempts to depict the future), but the book contains many illustrations that positively inspired a whole generation of children. Here, for example, book's cover illustration shows a spacecraft that has landed on Phobos, near a human base:

Mars. Welcome to paradise

Family walking around a human outpost on Mars in a vintage style poster "Mars. Welcome to paradise" by British freelance illustrator Mark Bell.

Exploring Mars with children by Jon Hrubesch

In "Captain Imagine: Tour of the Solar System" (2020) children's book by Karim Elmahmoudi Captain Imagine, a futuristic space explorer, takes young Emily and her brother Simon on a guided tour of our Solar System. The retrofuturistic illustrations for the book were created by American digital painter Jon Hrubesch. Here is one of the illustrations where Captain Imagine and the two children are exploring a Martian canyon.

Retrofuturistic Mars exploration base by Pascal Lee

In 2021 planetary scientist, the director of Haughton-Mars Project, Pascal Lee created a painting with the same, slightly updated scene of the first human exploration mission on Mars as in Chesley Bonestell's famous painting "Exploring Mars" featured in the 1956 book "The Exploration of Mars" by Willy Ley and Wernher Von Braun.

Highlighting Bonestell's legacy, Pascal Lee wrote: "In painting this new "Exploring Mars", I wanted to pay tribute to the grand master of space art and his creation of an iconic classic, but also update elements of the landscape and hardware in light of new knowledge gained about Mars in the intervening 65 years and evolutions in our thinking about future Mars exploration systems and human surface operations."

Comparison of Bonestell's (1956) and Lee's (2021) "Exploring Mars":

Terraformed Mars from human base on Phobos by David A. Hardy

In 1994 the famous British space artist David A. Hardy created several retrofuturistic illustrations of a human base on Phobos, the closest of two natural Martian moons, in front of a terraformed Mars. The illustrations were created as cover art for two separate books. More of Hardy's Mars art here.

"Terraforming Mars" as cover art for Arthur C. Clarke's book "The Snows of Olympus" (1994):

"Terraformed Mars" as cover art (there are several slightly different versions of this illustration) for Carl Sagan's book "Pale Blue Dot: A Vision of the Human Future in Space" (1994):

Mars outpost by Robert McCall

Picture of the Day 02/11/2021 - An early human outpost on Mars consisting of several landers and rovers by classical space artist Robert McCall.

СССР-2061 - a retrofuturistic vision of Soviet Union on Mars

Project "СССР-2061" is a community of Russian artists and writers envisioning Soviet Union in 2061 in an alternate reality. In 2011 they held their 1st arts contest asking participants to envision Soviet Union on Mars 50 years into the future. Here are some of the artworks from the contest.

Soviet spaceport in Valles Marineris on Mars by Igor Savin:

Domed soviet colony on Mars by Grinya Lesnoy:

Merry Christmas from Santa Claus on Mars!

Merry Christmas from Santa Claus on Mars! Retro art (1976) via Bridgeman Images.

Mars base in a crater by Sam Taylor

Picture of the Day 12/11/2020 - Retro style illustration of a human base in a Martian crater by digital artist Sam Taylor for his poster "Mars - Adventure Awaits". More of his art here.

NASA's base on Mars by Pat Rawlings

Picture of the Day 15/6/2020 - NASA's research base on Mars (1985) by classical space illustrator Pat Rawlings. More of his art here.

Family on Mars by Patrick Leger

Picture of the Day 14/4/2020 - retro style illustration with family exploring surroundings of a Mars colony by American illustrator Patrick Leger. Note the boy pointing at blue Earth in the Martian sky :) More of Leger's art here.

Nazi Moon base by Darren Tan

Singaporean freelance illustrator Darren Tan visualizing the conspiracy theory of a secret Nazi base on the far side of the Moon.

This alternate history science fiction myth was somewhat started by Rocket Ship Galileo, a 1947 young adult novel by Robert Heinlein, which features three teenagers who travel to the Moon and discover a secret Nazi base. Since then the "secret Nazi Moon base" cultural myth has been used in fiction frequently, including The Man in the High Castle novel (1962) by Philip K. Dick (and its recent TV series adaptation), Iron Sky movie (2012) and Wolfenstein: The New Order video game (2014). We should remember that Von Braun's V-2 rocket was the first man made object reaching outer space in June, 1944, and it was the base for both US and Soviet space programs. So the myth had some logical grounds.

Mars colony city by Bill Wright

Picture of the Day 6/3/2019 - Mars colony city under a dome by American retro space artist Bill Wright. More of his art here.

Mars dome interior by John Berkey

Picture of the Day 15/2/2019 - retro-futuristic illustration of what could be an interior view of a dome on Mars by classical future and space artist John Berkey. This illustration was done in 1975 as one of Otis Elevator Company adds. More of Berkey's art here.

Colony on Mars under plastic domes by Chesley Bonestell

Picture of the Day 3/2/2019 - "Colony on Mars under plastic domes" by classical space artist Chesley Bonestell, dubbed as "Father of Modern Space Art". More of his art here.

Retro style Mars rover by David A. Hardy

Picture of the Day 11/1/2019 - a small ATV type, retro style Mars rover in front of NASA's lander (1981) by classical space artist David A. Hardy. More of his Mars art here.

Mars colony by Bill Wright

Picture of the Day 16/12/2018 - Mars colony by American space artist Bill Wright. More of his art here.

Alien Martian canal by Mark Salwowski

Picture of the Day 11/10/2018 - Alien Martian canal and a city by Australian illustrator Mark Salwowski - a cover image for Lance Parkin's and Mark Clapham's book "Beige Planet Mars" (1998).

Retro Mars rover illustration by Jack Coggins

Picture of the Day 4/9/2018 - Retro Mars rover illustration by Jack Coggins from "Rockets, Satellites, and Space Travel" book (1958).

Vintage poster "Expedition Mars" by Kip Ayers

Vintage style poster "Expedition Mars" featuring a family exploring Martian landscapes by freelance illustrator Kip Ayers.
More of his illustrations here.