In the summer I was riding my bicycle here, there and everywhere in the city and visited the Dominion Observatory a few times. It's on the border of the Central Experimental Farm and is a short ride from my house.
You can read all about it at Wikipedia, but the short story is it was built in 1902, was used as an observatory until 1970, had its telescope transferred to the Science and Technology Museum in 1974, and is today used as office space for a branch of the federal government's Natural Resources Canada department. Construction of the wooden Mt. Lowe observatory was finished in 1894. It was destroyed in a wind storm in 1928.
One thing both observatories have in common is that they were accessible by an electric railway.
[This fascinating series of photos showing the observatory in various stages of construction was sourced from The Canadian Astronomical Society's page dedicated to the 100th anniversary of the Dominion Observatory.]
In 1908 the Ottawa streetcar system extended a double track line from Holland and Carling into the Central Experimental Farm. It ran parallel to Carling from Holland until it got to somewhere near the observatory where it then made a right turn and continued down to the main farm buildings. From there it looped around and came back. In 1924 a loop was installed at the observatory turn. The Ottawa streetcar system was finally closed down in 1959, and all traces of track at the observatory and farm have long disappeared, but I wouldn't be surprised if sections of the network of roads and paths on the grounds were originally streetcar roadbed.
A model of the Dominion Observatory would be quite challenging for me to build. This little building - building #9 on the site map, the Photo Equatorial - across the driveway from the observatory might be something more manageable. It's distinctive, small and captures the feeling of the stone construction and green dome of its big brother.
Not all the buildings on the site are early 20th century. Nearby is this abandoned 1960s modernist structure. I need to do a little research into what it was and why it's now derelict. It was probably very striking in its heyday.