Code
using GLMakie
with_theme(theme_light()) do
fig = Figure()
ax_main = Axis(fig[1,1:2])
ax_side = Axis(fig[1,3], xlabel = "y label", ylabel = "x label") # well, just flip these ones
Xs = Ys = -10:0.1:10
contour!(ax_main, Xs, Ys, exp.((-Xs'.^2 .- Ys.^2)/25))
obj = lines!(ax_side, Xs, exp.(-Xs.^2/25))
rotate!(obj, -π/2) # rotates your plotted object
ax_side.yreversed = true
fig
end