Simulation of Band-Pass Filter (RLC) in ngspice
Well, I've just realized the answer myself, with the help of Wikipedia.

What the RLC circuit does is to provide an harmonic oscillator between the capacitor and the inductor with a specific characteristic oscillating frequency.

If the input source oscillates in the same frequency and there is no dissipation of energy (zero resistance), they get into resonance and the voltage goes to infinity.

In my case, because the resistor has a low value (100 ohmns, above), there's nothing wrong with the voltage getting a peak of 30V RMS.